The Brain is a sapient, genetically-augmented laboratory mouse who seeks to take over the world along with his cagemate and associate Pinky. He's an intellectual genius and a skilled inventor. His stoic personality strongly contrasts with Pinky's goofy one, and he can be easily angered with Pinky at times. However, it has been shown that he cares about Pinky and enjoys his friendship. He also has an intense rivalry with the genetically-enhanced hamster Snowball.
Both Pinky and the Brain can be seen as graffiti when the film crew are making a movie Ready Player One.