Which actor played the role of Professor Proton?

Bob Newhart played Professor Proton on The Big Bang Theory.

Professor Proton is the stage name of Arthur Jeffries, a former children’s science-program host whose educational television show inspired Sheldon and Leonard when they were young. By the time he meets the physicists, Jeffries has retired from television and works entertaining children at birthday parties.

Newhart first appeared as the character in the season-six episode “The Proton Resurgence.” His dry, understated comic style made Arthur Jeffries an especially effective foil for Sheldon’s intense enthusiasm. The character returns several times, including after his death as a recurring imagined or dream-like mentor to Sheldon.

The role earned Newhart his first Primetime Emmy Award, for Outstanding Guest Actor in a Comedy Series, in 2013. He continued playing Professor Proton through The Big Bang Theory and later reprised Arthur Jeffries in Young Sheldon. The character is fictional, despite being presented as a familiar science-show personality from Sheldon’s childhood.