What is the name of Sheldon's long-time rival at Caltech?

Sheldon’s long-time rival at Caltech is Barry Kripke. Kripke is a plasma physicist and colleague who frequently clashes with Sheldon over science, status, and personal competition. Although their confrontations are usually played for comedy, Kripke is one of the recurring characters most clearly positioned as Sheldon’s professional rival.

Barry first appears in the second-season episode “The Killer Robot Instability,” where his robot, the Kripke Krippler, competes against the robot built by Sheldon, Leonard, Howard, and Raj. Their rivalry continues through academic disputes, workplace politics, and attempts to outmaneuver one another at Caltech. Kripke’s speech impediment, known as rhotacism, causes him to pronounce “R” and “L” sounds as “W,” making his taunts especially distinctive.

Leslie Winkle is another Caltech colleague and one of Sheldon’s archenemies, which can cause confusion. However, Barry Kripke is the character most commonly identified as Sheldon’s recurring professional rival.