Mother Brain

Mother Brain is one of Metroid's major antagonists, appearing in the main series while being heavily referenced by the Aurora units in Metroid Prime 3: Corruption. She is an a techno organic supercomputer AI created by the Chozo to govern their society. Unfortunately Mother Brain advanced her development to the point where she viewed the Chozo as weak obstacles that should be removed. To that end she gained control of the Space Pirate race and destroyed her creators, taking control of the planet Zebes before spreading her influence across the galaxy. Samus Aran would soon put an end to her rule, and again much later when Mother Brain reemerged with a new plan.

In terms of the MCD, Mother Brain is most infamous for being lauded by former user The Fifth as being Metroid's greatest villain while blaming Ridley for the "downfall" of the series.