The Clockwerk Brain is the part that possesses Clockwerk's mind and being. Without this part, Clockwerk would not be able to reactivate himself.
Sly 2: Band of Thieves
The brain is first mentioned in Sly 2: Band of Thieves, first in He Who Tames the Iron Horse. In Cabin Crimes, one of the cabins Sly enters hosts Jean Bison, who, at the time, is having a conversation with Arpeggio. A short way into the conversation, Jean Bison mentions his desire to buy the brain off of Arpeggio, but Arpeggio mentions that Jean Bison already has the lion's share of the parts, which consists of the Clockwerk Lungs and the Stomach.
Another mention is in Menace from the North, Eh?. When Sly exits the Safe House, Bentley talks to him through his Binocucom. Bentley informs Sly that if they are ever going to take a peek at the brain and steal it from Arpeggio, they will need to sneak aboard Arpeggio's Blimp.
- The Clockwerk Brain is briefly seen in Sly Cooper and the Thievius Raccoonus when Sly is using his cane to knock off Clockwerk's head.