Brain is an intelligent albino mole rat with an enlarged braincase, the brother of Keeng Ra'at.
He is the unlikely leader of the renewal cult in the ghoul town of Gecko and seeks to take over the world. He lives in an underground cave adjacent to the Gecko nuclear reactor. He loves Cheezy Poofs, and will ask the player to give him some if the player has any in their inventory as he can smell them.
In the short term, he seeks to build an alliance between Gecko and Vault City based on power from Gecko being sent to Vault City in exchange for medical research on how to "restore" the ghouls to humanity. The cult is symbolized by the ankh, and its members wear ankh necklaces. The renewal cultists seek to "renew," i.e. become human again.
 Interactions with the player character
 Interactions overview
Brain appears only in Fallout 2.
 Behind the scenes
- Brain, along with his "simpleminded" companion Zomak, is likely a reference to Pinky and the Brain, a now-discontinued television series about the attempts of a pair of mice to take over the world.
- The ankh necklace and the goal of "renewal" is a reference to Logan's Run.