Bob Newhart, the American stand-up comedian and actor best known for his two eponymous sitcoms, has died at the age of 94.

Newhart’s long-time publicist, Jerry Digney, said the actor died Thursday after a series of short illnesses.

Newhart guest starred in 6 episodes of The Big Bang Theory as Arthur Jeffries, or Professor Proton, Sheldon’s childhood TV hero. Newhart won the only Emmy award of his career for his first appearance on the show. He received another two nominations for his work on the show.

When Newhart spoke to The Hollywood Reporter in 2013 ahead of his first appearance on The Big Bang Theory, he explained two things were important for him to agree to Chuck Lorre's invitation to appear on the show. First, that his scenes be shot in front of a live studio audience, as he was accustomed to. Second, that his character be a recurring part.

Newhart carried his role as Professor Proton over to The Big Bang Theory spin-off Young Sheldon, appearing in the pilot episode and lending his voice to a further three episodes. A 2020 episode of Young Sheldon was Bob Newhart's final credited role.

A former accountant, Bob Newhart rose to fame as a comedian in the '60s. Known for his deadpan style and stammering delivery, Newhart had hit comedy albums in 1960 with The Button-Down Mind of Bob Newhart and The Button-Down Mind Strikes Back! A comedy variety show on NBC followed the next year.

The first of Newhart’s two hit TV shows debuted in 1972 with The Bob Newhart Show, which aired for six seasons on CBS and was produced by Mary Tyler Moore’s company, MTM Enterprises. Newhart starred as Dr. Robert “Bob” Hartley, a Chicago psychologist married to Emily (Suzanne Pleshette).

His second hit sitcom was the simply titled Newhart, which ran for eight seasons on CBS from 1982 to 1990. Newhart and Mary Frann starred as an author and his wife who run the Stratford Inn in rural Vermont. The final scene, in which Newhart wakes up from a dream in bed with his first TV wife, Suzanne Pleshette, has made the finale one of the most memorable in TV history.

Newhart also had a third self-titled sitcom, Bob, which ran for two seasons on CBS from 1992 to 1993. Apart from The Big Bang Theory, Newhart’s TV appearances later in his career included multi-episode roles on ER, Desperate Housewives, and The Librarians. He also starred in a series of TV movies in The Librarian franchise.

Newhart’s most memorable film role is probably as Papa Elf in the 2003 Will Ferrell holiday comedy Elf, considered one of the few classic Christmas films released this century. His other film credits included In & Out, Legally Blonde 2: Red, White & Blonde, and Horrible Bosses.

Newhart’s wife of sixty years, Ginnie Newhart, died last year at the age of 82. Ginnie was reportedly the one who suggested ending Newhart by combining it with the earlier show.