Like Byron Hadley, Brooks plays a much bigger role in the movie of Shawshank than the book. He's the original librarian, whose job Andy takes over. We don't see much of Brooks in the book; he gets paroled pretty early on and tossed out into the world to die a forgotten death. It's grim, but it also helps King emphasize what "institutionalized" means. Brooks can't survive in the outside world:
"In prison, Brooksie had been a person of some importance. He was the head librarian, an educated man. If he went to the Kittery library and asked or a job, they wouldn't give him a library card." (197)
The prison he carries around inside ends up being his defeat—Red needs to be careful not to share the same fate once it's his turn to be released.