The Big Bang Theory: 10 Characters You Totally Forgot Existed

Season 1, Episode 4: The Jerusalem Duality

Due to Sheldon's crippling narcissism and urge to prove everyone wrong, he has earned himself a legion of enemies including Leslie, Barry, Priya, and Wil Wheaton.

But one rival everyone has forgotten about (obviously apart from Sheldon) is Dennis Kim. When Caltech's chairman, Dr Gablehauser, crossed paths with this teenager, he recognised Dennis was a child prodigy and thus, immediately recruited him into the university's PhD program.

Despite his brief appearance, Dennis has the potential to be Sheldon's arch-nemesis. Not only is he one of the few characters smarter than Sheldon, Dennis is over a decade younger. He's also the youngest recipient of the coveted Stevenson prize - a title which Sheldon originally owned.

Just to rub further salt in the wounds, Dennis informed Sheldon that his research on string theory is a dead end. Although this sort of antagonism usually causes Sheldon to double-down, he was so rattled by Dennis' claim, he abandoned his research and immediately sought a new field of study. Even though Will Wheaton and Barry have gotten the upper hand over Sheldon repeatedly, nobody made him feel like an idiot the way Dennis did.