Sheldon is a theoretical physicist from Caltech who rooms with Leonard in apartment 4A of their rundown apartment building, in which the elevator always seems to be out of order. He is Leonard's best friend and colleague, who appears to have obsessive–compulsive personality disorder, beginning with suspicion of it in episode S01E02. A prodigy, Sheldon possesses a Master's degree and 2 PhDs. Recently, he has switched disciplines from bosonic string theory to heterotic string theory and has reconciled the black hole information paradox using a string network condensate approach. Like Leonard, he keeps a whiteboard in the living room for scientific theories, especially for his work on string theory. Unlike (more...)