History of the Metroid species

The Metroid species are the titular creatures of the Metroid series. Below is the full history of them.

Creation and later discovery

A Metroid, likely the first in the universe, being released in Memory 5/11 of the Chozo Memories.

The Metroids were created by the Chozo of the Thoha tribe during an underground expedition on the planet SR388. The Thoha Chozo came across a dangerous lifeform that they referred to as the "X Parasite", which the ancient race deemed as an "evil" due to their ability to infect, assimilate and copy the features of other creatures. To combat this threat, the Chozo found themselves obliged to engineer a predator that could take on the X; another parasitic creature they denominated "Metroid". Appropriately, their name roughly translates to "Ultimate Warrior" in the Chozo language.

Metroids being released and draining the life force of X Parasites and infected Hornoads in Memory 6/11.

This was successful at first, as the Metroids proved to be an effective counter of the X-Parasites thanks to their ability to drain a prey's life force, which the X had no defense against and helped put their population into check. However, as time passed, the Metroids started evolving into bigger, more hostile forms, presumably due to the effects of the Aeion within the caverns of SR388. This came as a surprise to the Thoha, who found themselves unable to control them any further. The Metroids eventually started attacking their creators, who seemingly could do little against their own creations.

Metroids molting into their Alpha stage and attacking their creators in Memory 8/11.

This led the Thoha to take desperate measures with the aid of the warlike Mawkin tribe, using a special mechanism to flood most of SR388's underground caves with a dangerous purple liquid that prevented Metroids from passing through, keeping them trapped into the depths of the planet and limiting their propagation to an extent. However, this did not prevent the Metroids from becoming the apex predator of SR388, as they kept growing into even bigger, stronger forms, including even a queen that could increase their numbers through reproduction. The Thoha began plans to destroy SR388 in the hopes of eliminating both the Metroids and the X, only for them to be betrayed and massacred by the Mawkin. The Mawkin's leader, Raven Beak, coveted the Metroids for their potential as bioweapons and planned to return to SR388 to capture them, but the infection of one of his soldiers by the X prevented his plan from being carried out.

The Chozo flooding caverns with purple liquid using a Chozo Seal to keep Metroids trapped in Memory 9/11.

Much later, the Metroids were discovered by the Galactic Federation and drew the attention of the Space Pirate organization, who tried to use them as bioweapons against galactic civilizations. For that reason, the Galactic Federation considered the Metroids as a threat to intergalactic peace, even declaring war against the parasitic creatures, but their own forces turned out to be ineffective at stopping this new menace. As a result, the bounty hunter Samus Aran was eventually hired to exterminate Metroids on numerous missions across various planets.

Metroid/Metroid: Zero Mission

A Metroid in the original Metroid.

In Metroid and its remake, Metroids were stated to have been originally discovered by the Galactic Federation while researching SR388. This initial encounter gave a glimpse of the species' powerful abilities but despite the Federation suffering casualties on their side, the latter were nonetheless successful in capturing at least one Metroid. Soon afterwards, the Space Pirates boarded the Space Research Vessel Marina in which the Metroid specimen was being transported and stole it, taking it to their base deep within the planet Zebes. Inside their headquarters, the Pirates began to multiply the creature's numbers by exposing it to beta radiation. After several attempts by the Federation to defeat them with frontal assaults, Bounty Hunter Samus Aran was tasked with singlehandedly infiltrating the Space Pirate base Tourian and destroying the Metroids there, as well as Mother Brain. She was the only one to complete this mission.

A Metroid in Super Metroid.

Metroid Prime

A Metroid appearing in Metroid Prime.

Fleeing from Zebes, the Space Pirate frigate Orpheon carrying Metroid specimens eventually landed on the planet Tallon IV. Exposure to the planet's atmosphere triggered changes in the Metroids' physiology, becoming a new breed that would be known as Tallon Metroids. These Metroids are initially smaller and less durable than those encountered on Zebes; while they retain the weakness to the Ice Beam, Samus is now capable of killing them with any weapon in her arsenal, though they take extensive amounts of time and firepower for her to do so. When consuming even the slightest amount of life energy, they will convulse and suddenly expand in size, reaching roughly the same mass as the Metroids encountered on Zebes. If Samus carries enough Energy Tanks in her suit, she can also let Tallon Metroids drain her Power Suit's energy until they explode from overfeeding.

Despite these initial flaws, Tallon Metroids react strongly to the mutagen Phazon discovered by the Pirates on Tallon IV. This prompted the Pirates to experiment with their specimens, leading to the creation (both intentional and unintentional) of powerful aberrations in the Metroid species: 'Hunter' Metroids, which have red translucent membranes and two long range energy-siphoning tentacles, 'Fission' Metroids, who's individuals can split into two separate entities when attacked, and finally the heavily Phazon-mutated Metroid Prime. Though this last mutant's origins are kept largely ambiguous, a theory can be found here. All the Metroids encountered on Tallon IV, save for the Metroid Prime, can be dispatched with a single Power Bomb, contrary to other breeds seen elsewhere which require numerous bombings.

Danny Richardson designed several Metroid forms that were not included in Prime.

Metroid Prime Hunters: First Hunt

Samus undergoes personal training in holographic arenas where she combats several holograms, some of which are in the form of Metroids. Two types of Metroid targets are loaded up inside the arenas: Tallon Metroids and what appears to be an emaciated variant bearing a striking resemblance to Mochtroids encountered later on in the series; the latter hologram is never given a proper name.

Metroid Prime 2: Echoes

In Metroid Prime 2: Echoes, the Space Pirates imported Metroids to planet Aether. The planet's environment and stimuli seemingly caused the creatures' membranes to gain a red coloration. Other than this adaptive change, they possess the same attributes as the Metroids from the previous game. The Space Pirates have landed on the planet in the hopes of finding more Phazon energy and to continue their research on the Metroid species.

The Ing, the dominant race of Aether's dark dimension, eventually take control of many Tallon Metroids through darkling possession, creating a unique strain called Dark Tallon Metroids. They feature thick, ridged carapaces covered with numerous orange eyes instead of the smooth, transparent membranes seen commonly in prior Metroids. The transformation grants them far more durability against both conventional and dark matter-based weapons, but consequently gain a high sensitivity to the Luminoth's weaponized Light of Aether. The darkling Metroids are used as soldiers in the Ing Horde patrolling Aether and Dark Aether; the Metroids' animal mindset is allegedly replaced with the high level of intelligence of the Ing controlling them, increasing their threat level.

The Space Pirate base in Agon Wastes contains a room filled with artificially-created Metroid Cocoons. These organic storage chambers carry Infant Tallon Metroids that can instantly grow into the red-colored Tallon Metroids when they make contact with Phazon. This small breed cannot yet absorb energy and instead aggressively ram their targets to damage them. The Space Pirates seem to use this Metroid strain as portable energy sources that can be easily and safely transported in large quantities.

Metroid Prime 3: Corruption

In Metroid Prime 3: Corruption, four additional mutant strains of Metroid are introduced. They all originate from Tallon Metroids that were either heavily exposed to Phazon energy or were infused with the mutagenic during the egg stage. Their importation on a Pirate Homeworld seems to have also played a role on the creation of these new breeds. The Space Pirates are intent on progressing further with their Metroid experiments and research in order to use them for the plans of their new leader, Dark Samus.

The first encounter are with the Phazon Metroids kept in a Pirate lab on Elysia. These powerful, blue-membraned organisms can not only leech life energy but also launch electrical Phazon energy at their prey as well as become intangible, allowing them to traverse without hindrance through barriers, solid matter and weapon fire. The Phazon Metroid's infant stage is the Miniroid, an extremely frail, non-aggressive breed that travels in massive groups in order to increase its chances of survival. Despite the Miniroids' initial weaknesses, they ultimately grow into the dreaded Phazon Metroids prior to metamorphosing into one of the following forms: the Hopping Metroid or the Metroid Hatcher.

Hopping Metroids lose many of their larval form's abilities, but develop sharp limbs and a highly resistant exoskeleton. Their new bodies allow them to enter an amplified state known as Hypermode that multiplies their durability and attack power. They can also spit Phazon venom from their mouths as well. The Metroid Hatcher maintains its flight capability while growing a Phazite-like shell and growing energy-siphoning tentacles. They are capable of spawning live Phazon Metroids from their oral cavity.

A massive population of mutated Metroids are found on planet Phaaze, the source of all Phazon in the universe. Though their presence on the planet may seem strange at first sight, Phaaze's great distance from all other locations in the Metroid series makes it likely that the Space Pirates and/or Dark Samus imported the species upon their arrival.

Metroid Prime 3: Corruption presented various scan data found on the Pirate Homeworld that finally explained the many changes in Metroid physiology as the result of being exposed to different atmospheres and other stimuli such as Phazon. The same room containing these scans features three empty tanks, each referencing a breed from Tallon IV, Zebes and SR388. A close inspection of a dissected Metroid corpse reveals it to be none other than a Dark Tallon Metroid from Aether.

Metroid Prime: Federation Force

The Space Pirates maintained a supply of Metroid Eggs and Larvae, multiplying the latter in a former medical laboratory on Talvania. All of the Metroids present, including the Pirates themselves, were enlarged with the Amplification beam. The Galactic Federation caught wind of this operation and tasked the Federation Force with destroying the facility via a self-destruct mechanism inside. General Alex Miles also asks the Force to, if possible, bring back some Metroid Eggs for study. While this is an optional bonus objective in-game, it is considered canon. At the end of the game, the Federation-hating Bounty Hunter Sylux infiltrates a GF laboratory, and causes a Metroid Egg in captivity to hatch.

Metroid II: Return of Samus/Metroid: Samus Returns

An Alpha Metroid in Metroid II.

A Gamma Metroid in Metroid II.

In Metroid II: Return of Samus, seeing the dangers the Metroids posed to the galaxy, the Galactic Federation sent the Special Squadron to SR388 to wipe out the hostile lifeforms. After two failed attempts by the Federation's army to eradicate the Metroids on their home planet of SR388, they called on Samus Aran to deal with them as she was the only person able to survive several encounters with the creatures. It was in this specific mission where the natural life cycle of the species was first discovered, with the most well-known form of Metroids from previous incidents revealed as being merely the larval stage.

Samus' goal was to explore SR388 and hunt all remaining Metroids down one by one. As she progressed further into the planet, the Metroids continued along their natural life-cycle, eventually culminating in the Omega Metroids. Samus eventually reached the Metroid nest and several new Larva Metroids suddenly appeared before she destroyed them and the Queen Metroid, seemingly eradicating the species once and for all.

After the Queen was destroyed, an infant Metroid hatched and imprinted on Samus as its mother (thus raising questions as to the true instinctual intelligence of the average Metroid). Because of Samus's efforts, this infant was the last surviving Metroid in the galaxy. It helped Samus leave SR388, and she took it back to the Federation Academy for further research.

Evolving into Alpha Metroids

The unlockable Chozo Memories in Samus Returns shows the beginning of the Chozo colony on SR388 and the eventual creation of Metroids in response to the X Parasites. The memories also reveal the fate of the Chozo on the planet after the Metroids began to evolve.

Super Metroid

"The last Metroid is in captivity. The galaxy is at peace..."

"It is said that Metroids are life forms created by an ancient civilization. Metroids engulf living creatures and absorb their energy. They are very intelligent and quick to reproduce."

Multiplied Metroids in Super Metroid.

The Infant Metroid has grown into a Giant larva.

In Super Metroid, the Infant Metroid that had imprinted on Samus was studied by scientists on Ceres Station; it was found that the Metroids' potential as beneficial creatures was as great as their destructive powers. Mere minutes after Samus left the station, the Space Pirates besieged it, killing everyone on board. Ridley stole the hatchling, taking it back to the Space Pirates' rebuilt base on Zebes.

The Space Pirates quickly used beta-rays to multiply Metroids out of the last infant. However, this usual method would not be enough for the organization this time; the Pirates were anxious to resupply themselves with as many Metroids as possible, thus pushing them to attempt at genetically cloning the hatchling (and possibly the multiplied specimens) alongside the beta-ray exposure. This ambitious method would end in disappointment: in Maridia, Samus finds the cloned failures named Mochtroids. As their name suggests, these clones are a mockery of the true multiplied larvae that filled Tourian's hallways. Though the Mochtroids could still leech life-energy, the siphoning itself was poor, their membranes were extremely frail and they lacked the strength to properly grip onto prey.

The Metroids found in Tourian could only be dispatched by freezing them then followed with blasts from concussive weaponry. Power Bombs could be used to harm them without the use of the Ice Beam, but did very little damage; in addition to having a slow rate of drops between each Power Bomb, they were far less reliable against Metroids this time around.

Samus eventually finds the missing Infant Metroid, however several unknown factors caused it to mutate into a Giant Larva. Not recognizing Samus at first, the Metroid began devouring her life energy only to remember at the very last moment, causing the creature to flee the scene in shame. At the end of the game, the Giant Metroid sacrificed itself to save Samus by attacking and leeching Mother Brain's energy. It then demonstrated the life-saving properties that could have benefited galactic civilization: transferring energy to living beings instead of simply absorbing it. As it re-energized Samus' depleted Energy Tanks and gave her a new weapon stolen from Mother Brain, the Metroid was killed by none other than the resurrected Pirate leader herself. Its demise meant the apparent extinction of the entire Metroid species; it also demonstrated the Metroids' ability to show compassion.

Metroid: Other M

The Infant Metroid restores Samus' health in a flashback of Samus' recent past.

After Samus Aran completed her second mission on Zebes, she spends a great deal of time in thought, reliving the death of the Baby at the hands of Mother Brain. Adrift in space and in memories, she receives a message codenamed "Baby's Cry", reminding her of her lost "child". Following the signal, Samus arrives at the BOTTLE SHIP.

In the Cryosphere, Samus finds a deceased Gigafraug showing signs of Metroid predation. Samus has doubts since not only would Metroids perish in the Cryosphere's cold temperatures, they were extinct thanks to the efforts of both the Space Pirates and herself.

Soon afterward, MB, posing as Madeline Bergman, tells Samus about "Project Metroid Warriors", in which Metroids were cloned from the Baby's particles that landed on Samus's Power Suit and are located in Sector Zero. She also explains that they made an AI of Mother Brain's intelligence to control them.

Samus heads to Sector Zero but stops short as an Infant Metroid pops up in front of her, reminding her of the Baby. When Samus decides to kill the Metroid, Adam shoots her in the back; the Infant sees her as food, but is also shot.

Adam explains that the cloned Metroids that have reached the mature larval stage are likely to have been re-engineered to remove their vulnerability to cold, making them virtually unstoppable; this also confirms that the dead Gigafraug Samus found earlier was indeed the subject of Metroid predation. He also states that the breeding project was named after him, though he was not actually involved in the project. He was petitioned for the authority to create the project, but he refused. However, scientists co-signed it to get the project running.

Adam shot Samus earlier to prevent her from interfering with his next course of action: because the Metroids are immune to Samus' weaponry, Adam goes to activate a self-destruct protocol on Sector Zero by causing severe damage from within, which detaches the sector from the station before the explosion. Seeing this as a suicide mission, Samus attempts to convince him to let her destroy the Metroids, but Adam ignores her, saying that she has work left on the BOTTLE SHIP. Adam succeeds in his mission to destroy the Metroids at the cost of his own life.

However, a Queen Metroid was kept in another part of the BOTTLE SHIP. It not only attacks Samus, but launches several other Metroids. Ultimately, Samus is forced to resort to an old tactic and uses a Power Bomb in the belly of the beast. it is currently unknown how MB succeeded in making an Infant Metroid reach the Queen stage outside of SR388's environment.

Metroid Fusion

Samus fighting the Omega Metroid in Metroid Fusion.

Metroid Fusion takes place shortly after Other M and it is "Metroid IV" in the timeline. On planet SR388, the Metroids had been the top predators, and with them gone the ecosystem was thrown completely out of balance. Samus was hired to protect some Federation scientists who were studying the recovery of the SR388 ecosystem. While they were on the planet, Samus was infected with an X Parasite, a highly dangerous organism who's species is quickly ravaging the planet. She was rushed back to Federation Headquarters with a minimal chance of survival. It had recently been discovered that the Metroids were the sole predators of the X Parasites; without the former to keep them in check, the X are rapidly reproducing and infecting all forms of life, taking their hosts' DNA in order to mimic them before moving on to their next host. Using this information, the Federation saved Samus by injecting her with a Metroid vaccine made from a DNA sample of the deceased hatchling.

With Metroid DNA fused with her own, Samus had gained immunity to the X Parasites and was now capable of absorbing them in their pure forms by merely touching them. She had essentially become the "Ultimate Warrior", making her the only being capable of combating the X and their horrific mimicries of countless bioforms that had now spread out into the Biological Space Laboratories in orbit above SR388. If a single X Parasite were to gain access to a host capable of piloting a space-faring vehicle, a galactic plague would be inevitable. The presence of Metroid genes in her body were not without consequence however, as she had gained the species' vulnerability to sub-zero temperatures, a weakness the X would repeatedly exploit throughout her mission.

Later in Metroid Fusion, it was revealed that the Federation had a secret Metroid breeding program going on (see Restricted Lab), presumably based on clones of the last Metroid. Contrary to the Metroid project on the BOTTLE SHIP, it would seem that the program on the BSL was intended for benevolent purposes. In any case, this program was destroyed by a powerful X Parasite mimicking Samus known as the SA-X. The entire laboratory was detached from the station and ejected into space just after Samus escaped, completely destroying the Federation's research. However, one Infant Metroid had escaped and advanced to Omega level. Worthy of note is the difference in size between this Metroid and the Omegas found on SR388, the latter of which were only slightly taller than Samus. The creature was blocking her path towards escaping the BSL; moments earlier she set course for the station to enter SR388's atmosphere and detonate in order to destroy all X Parasites onboard the BSL and the planet below. The Omega Metroid severely wounds Samus and the SA-X, the latter which had seemingly been drawn to the presence of both Metroids. Samus takes the opportunity in absorbing the SA-X, healing her completely and acquiring the Ice Beam which she uses to kill the Omega Metroid before boarding her ship.

Metroid Dread

Having learned of the destruction of SR388 and Samus' Metroid Vaccine, Raven Beak conspired to lure Samus onto his base on ZDR in order to recreate the Metroid species from her DNA. To do so, he provided evidence of the X's survival to the Galactic Federation and reprogrammed the EMMIs sent to investigate, forcing Samus to discover what happened.

Following her first confrontation with Raven Beak, Samus experienced what ADAM referred to as a "dramatic physical change" of unknown origin, which would later be accompanied by the manifestation of strange new abilities. While not fully aware of them at first, she eventually came to discover that she could drain the life energy of other beings (even machines) with just a touch. According to ADAM (in fact Raven Beak in disguise), the Metroid vaccine's transformative effect had been previously suppressed by Samus' Thoha DNA, but the encounter with Raven Beak had undone the suppressive effects. Consequently, she was on the verge of becoming not just a Metroid, but the most powerful Metroid to have ever existed.

Samus becomes a Metroid.

After nearly being defeated by Raven Beak, who was preparing to clone Samus in order to build an unstoppable army, the Metroid DNA fully activated, causing Samus to mutate into a Metroid-like form and letting her drain him to near death. Though her newfound strength allowed her to destroy Raven Beak completely following his infection by the X, she was warned by ADAM that in her current state attempting to operate her ship would simply drain its energy, leaving her stranded on the doomed planet. However, the X-infected Quiet Robe allowed himself to be absorbed by Samus, stabilizing her transformation and allowing her to escape.

It is unknown whether or not Samus retained her Metroid powers following her stabilization.

See also

• Biography of Samus Aran
• History of the Space Pirates