Quadraxis

Quadraxis was a massive security drone created by the Luminoth to protect the Sanctuary Fortress. However, the Ing conquered the fortress, and posessed Quadraxis, taking him to guard the Ing Hive instead. After Samus Aran landed on Aether and restored power to Agon Wastes and the Torvus Bog, she went to the Sanctuary Fortress to restore power to it as well. In turn she entered the Ing Hive and defeated Quadraxis.

Battle
Quadraxis, in its first form, uses the Annihilator Beam (normal and charged), missiles, and a tornado attack similar to the one used by the Quads also found in Sanctuary Fortress. The only difference is that while the Quads spin around the arena trying to ram Samus, Quadraxis will stay in the middle of the arena, attempting to suck her into it. There are multiple ways to dodge this attack. One way to avoid this attack is to get on the far edges of the arena when it begins to start this attack; another is to shoot it's feet with a charged beam or Screw Attack into it. Quadraxis is damaged by destroying its knee joints with missiles or Super Missiles or its foot weaponry with the Boost Ball or Morph Ball Bombs. Once its main body is crippled its head will detach and fight on its own. The head will use a shielding device which receives energy from the body. Using the Echo Visor, Samus must destroy the shield transmitter on the body and attack the receivers on the head. Once one receiver is destroyed, Quadraxis will try to re-establish the lost link, and summon Dark Quad MB and CM robots in the process. The best way for Samus to deal with these is to destroy the heads and keep moving so the bodies cannot spin into her, because if she takes the time to completely destroy the Quads, Quadraxis will re-establish the link. Once all the receivers are destroyed, Quadraxis's final form will engage. Samus must then attack the head unit until it is stunned, at which point it will slowly circle its body. Quadraxis's final form is defeated by using the legs as ramps, using the Boost Ball to boost onto its head, attaching to the head unit with the Spider Ball, then moving into one of the two Bomb Slots on its head and using a bomb. Once bombs are dropped in both slots, Quadraxis will die, leaving behind the Annihilator Beam. Once the Annihilator Beam is acquired, several platforms rise in the center of the room with Spider Ball Track on the side, allowing Samus to escape the temple.

Trivia

 * Disassembled parts of Quadraxis can be seen scattered throughout the Fortress Temple entrance, suggesting that the Luminoth were in the process of making more than one.
 * This could also suggest that the parts were already on Dark Aether when it formed, and the Ing somehow managed to properly assemble it; the parts lying about on Light Aether could suggest that the Luminoth didn't manage to finish Quadraxis before their defeat, or that they didn't want another Quadraxis to be possessed by the Ing.
 * Quadraxis is arguably the largest boss in the Metroid series. Kraid may come a close second. Kraid may or may not be taller but Quadraxis is definitely wider and would most likely be heavier as well.
 * Quadraxis' head when exposed is similar to an Aurora Unit. This may suggest that it is a Luminoth variant of the Mother Brain created by the Chozo, and the Galactic Federation-created Aurora Unit.
 * In early screenshots, Quadraxis was blue with green armor. Another notable fact is that even though it briefly changes color when possessed at the beginning of the battle, it is the only possessed creature in the entire game to maintain its original color scheme.
 * Probably because of the Ing controlling it, Quadraxis is most vulnerable to the Light Beam.
 * The music heard when battling Quadraxis is a remix of the Ing battle theme. Here is a link to the music heard when battling Quadraxis:.
 * Samus can reach Quadraxis without the Ing Hive Keys, by Sequence Breaking. SkyTown Concept Art.jpg
 * Unlockable artwork for SkyTown in Metroid Prime 3: Corruption shows a strange structure, with a Quadraxis-style head atop it.