The Young Sheldon Episode You Likely Forgot Starred Professor Proton

"The Big Bang Theory" aired its final episode in 2019, but the legacy of the nerd-centric sitcom lives on thanks to the spin-off "Young Sheldon." As the title suggests, the prequel series follows the titular mighty little man (Iain Armitage) as he grows up in small-town Texas, surrounded by his family, classmates, professors, and the few people he decides to accept as his friends. While some viewers have noticed inconsistencies between the events of "Young Sheldon" and "The Big Bang Theory," both shows share characters who have influenced Sheldon in some way, including the scientist he grew up idolizing.

Anyone who's watched "The Big Bang Theory" will be familiar with Professor Proton (played by Bob Newhart). The TV scientist — along with his puppet sidekick Gino the Neutrino — inspired Sheldon to become a theoretical particle physicist in the first place, after all. Proton also interacted with Sheldon in a few episodes of "The Big Bang Theory" back in the day, most notably as a ghostly Jedi who gave him advice. The character can also be found in "Young Sheldon," albeit not in the form of a supernatural hologram.

Professor Proton appeared in a Season 3 episode of Young Sheldon

Professor Proton is mentioned frequently in "Young Sheldon," making it clear just how much of an influence he had on the titular character's childhood. Furthermore, Sheldon tends to watch the scientist's show every afternoon, often causing conflict with his father, who prefers watching football games over educational programming. Despite mostly being mentioned in passing throughout "Young Sheldon," however, Proton did have a cameo in the "Teenager Soup and A Little Ball of Fib" episode (per IMDb), which aired in 2019. 

The Season 3 episode sees Sheldon lie to his parents so he can stay home from school and skip his swim test. He believes that the pool is full of germs, and he doesn't want to risk catching a deadly disease. Proton's show can be heard in the background during one scene, with the scientist (once again voiced by Bob Newhart) instructing viewers to "suck on eggs." 

Professor Proton has appeared in three episodes of "Young Sheldon" (via IMDb) at the time of this writing, but his cameos were so brief that some fans probably missed them.