Professor Robb Rothman is an elderly theoretical physicist at the university, who was forced to step down and possibly in the early stages of senility (and may possibly have also gone insane). He is prone to appearing naked in public, except for a hat, and seems to believe he is invisible. According to Leonard, Professor Rothman is an exemplary case for the propensity of a theoretical physicist to "snap".
His character was first mentioned by Kripke when he informed Sheldon and Raj that "Professor Rothman urinated in the Particle Physics Lab again". His retirement party (after being moved up) was scheduled to be on a Friday at 5 o'clock and to have a pot luck, for which Raj wanted to make his famous popovers. ("The Beta Test Initiation")
Rothman's retirement left a vacant office, the possession of which became a point of contention between Sheldon and Kripke until the matter was resolved by a competition, wherein the spoils went to the former. Though, the professor still visits his old office, despite no longer having a claim to it, so as to peruse an issue of the Journal of Physics G: Nuclear and Particle Physics. ("The Rothman Disintegration")