The N'kren are a starfaring race mentioned only in Luminoth Lore in Metroid Prime 2: Echoes. It is likely that they also met with the Chozo, Ylla and Reptilicus. Like the Ylla, they have yet to be seen in person in the Metroid series.
"It is told that the Luminoth were not born of Aether, but of the stars. In the early days, we roamed the greatness of the void, bathing in the glorious light of a thousand stars. We met a vast number of enlightened minds... the N'kren, the Ylla, and the Chozo among them. Each of them, we found, had claimed a homeworld and formed a deep bond with it. In time, we decided to do the same."
|Sentient Species in the Metroid series|
|Human | Space Pirate | Craftsmen | Kriken | Luminoth|
|Reptilicus | Diamont | Elysian | Ing | ancient Bion race|
|Alimbic | Chozo | N'kren | Phrygisian | Enoema | Vhozon | Ylla | machine race |
"Elfin" | "Simian" | "Ceratopsid" | "Space Dragon"