The Brain is an object in the original TimeSplitters, found in the Planet X mission. It is in a protective glass or Perspex case. Sebastian Photon and Angel Perez go to Planet X to return the hostage cyberbrain the alien inhabitants stole. It is also used as the BagTag/Knockout item in the Compound, Planet X, Spaceship, Streets and Warzone levels, as well as in the Alien tile set in MapMaker.
The Brain makes a minor appearance in TimeSplitters 2. In one of the challenges in the TimeSplitters 'Story' Classic, copying the form of Story mission from the original TimeSplitters, namely Badass Buspass Impasse, Badass Cyborg must collect his spare brain on the other side of Streets.