Arthur Jeffries, Ph.D.—a.k.a. Professor Proton— was a down-on-his-luck former children's science show host who's hired by Sheldon and Leonard to entertain them. Professor Proton was known for demonstrating scientific principles using everyday objects. Proton often would dispense the aphorism, "There is no problem you can't solve, if you use your noggin’.” The Professor Proton theme song lyrics read, "Grab your goggles, put your lab coat on. Here he comes, Professor Proton." His beloved puppet sidekick – Gino The Neutrino – was a blue, anthropomorphized elementary particle with an Italian accent, a mustache, and gondolier costume under a lab coat. It is later revealed that Jeffries hated the puppet after his puppeteer slept with his then wife.
It turns out that Sheldon and Leonard grew up on his show, and that made them want to become scientists. When Sheldon and Leonard learned that their childhood idol was in the business of doing private science shows for paying customers, they seized on the chance to hang out with the guy and do some experiments. Unfortunately, the good professor was under the impression that he was going to be doing his act for kids, as opposed to grown men who were already respected scientists.
When they met him -- in the stairwell, as they'd neglected to tell the 83-year old that the elevator didn't work -- Sheldon freaked him out with his excitement at being allowed to call him “Arthur” and getting as close to him as he wanted without his mom telling him he would hurt his eyes. The Professor even went so far as to ask Leonard if Sheldon was dangerous. Leonard simply responded that “he’s a genius”. After Sheldon took his bag and offered to race him up the stairs, the Professor asked Leonard if “the blonde” was really his girlfriend. When Leonard said yes, he told him that he’s the one who’s a genius.
Once he was sitting awkwardly on the couch trying to figure out why he was there, Leonard told him they just thought it would be nice to hang out with him and hear about his life. According to Jeffries, when the Professor Proton show ended, he couldn't find work in Hollywood, and he was seen as a joke among serious scientists in spite of his very real PhD from Cornell, so he ended up on the birthday party circuit, building potato clocks and sucking eggs into Erlenmeyer flasks for the amusement of children (and Penny). He seemed baffled that two grown men, physicists even, wanted him to put on a kids science show. He did though, or at least part of one, reacting with growing dismay to Penny’s lack of science experience and general ditziness. He thought of himself as a failure and the final straw, that two full-grown weirdos apparently adored him enough that they wanted him to do a show in their living room, was enough to push him over the edge and declare himself retired. Jeffries revealed: He’s 83, other scientists think he’s a joke, he has a potato in his suitcase and the puppeteer that controlled his sidekick Gino also did his wife. So, what good has it done?
Sheldon went to get his autographed photo of Professor Proton and he and Leonard explained how his show was the reason that they and others like them got interested in and pursued careers in science. Sheldon credited Jeffries with giving him not only a role model, but a friend of sorts, during a difficult time in his life. He claimed that without Proton to guide him, he could have ended up anywhere—and so could have all of the young future scientists who tuned into Jeffries' show. Whatever amazing discoveries Leonard and Sheldon make are, in a way, Jeffries' discoveries too.
Professor Proton was so touched that his pacemaker malfunctioned and Sheldon's awesome day got even better when he got to ride in the ambulance with his idol and serenade him with the latest rendition of "Soft Kitty." Unable to perform for a birthday party the following day, Jeffries bestowed his mantle upon Sheldon and asked him to fill in -- he could be Professor Proton, Jr.
In "The Proton Displacement", Sheldon, Amy and Leonard spot Professor Proton at the drug store. Sheldon reintroduces himself since he doesn't think that he'll remember him because of his advanced age (though he does remember Sheldon). He also introduces Amy as his girlfriend that astonishes Professor Proton. Amy then shakes his hand and then notes that they have the same orthopedic shoes. She can't believe that she dresses like a celebrity. Professor Proton then understands how he has a girlfriend. Later, Leonard then gets an email from Professor Proton. He is working on a paper about nano-vacuum tubes and he wants Leonard to read it. Sheldon gets jealous.
Amy tries to tell Sheldon that others consider him annoying. Sheldon goes over to Professor Proton and apologizes to him. He also suggests that Professor Proton let him read his paper. He declines, and Sheldon unintentionally gets on his bad side by calling him a "washed up has-been".
Leonard and Professor Proton are in Leonard's lab with Leonard telling him that if people had told him thirty years later he would be working on science with Professor Proton, he would not have believed them. Arthur quips that if people had told him that people would still be calling him Professor Proton at the age of 83, he would not have stopped smoking. Sheldon shows up with his new friend and colleague, Bill Nye, the Science Guy. Sheldon tells Arthur that he replaced Arthur with a newer model. Bill Nye finds it an honor to meet Arthur Jeffries since his show was based on Professor Proton. Arthur snaps as him that that was what he had told his lawyers, implying that they have had a lawsuit concerning the originality of Bill Nye's science show. Professor Proton objects to Bill Nye inspecting his latest project. "Haven't you stolen enough from me? Back off, Bow Tie!" Professor Proton also asks Leonard why he puts up with Sheldon. He gets Leonard to admit that Sheldon is the smartest person he has ever met, that he is a little broken and he needs him and Leonard needs Sheldon.
Later in Apartment 4A, Arthur Jeffries visits Sheldon. Sheldon is surprised that he was there. Arthur asks him to look at his paper and Sheldon tells him that it would be an honor. Then Sheldon adds that he already hacked into Arthur's email account and read it. Arthur asks what he thinks. Sheldon starts with he thinks its pathetic using his birthday date as a password. The paper, Sheldon feels is inspired. Arthur thanks him. Sheldon invites Arthur for tea; he gently says he needs to go, but changes his mind after seeing Penny again. After Sheldon describes his eighth favorite episode of the Professor Proton series, was the Alka-Seltzer rocket, Sheldon runs off to get some Alka-Seltzer so they can recreate the experiment. Arthur then asks if Penny has any single grandmothers. Penny does, however; they are married. He then wonders if they are happily married. Penny looks non-committal (comme ci, comme ça) response, which makes Arthur happier.
In the episode "The Proton Transmogrification", our beloved professor passes away and Sheldon sees him reappear, he is then regarded as Sheldon's Obi Wan though Arthur is not aware about the Star Wars' characters. First he appears wearing his usual business suit and following Sheldon's Star Wars comments his clothes change to Jedi robes. Arthur has fun with his light saber until he cuts himself. In a later dream, Arthur gives Sheldon the advice to always have a prenup and appreciate those around him before they pass away as he has. His final advice is for Sheldon to not waste his life away watching the same movies over and over though Sheldon misses the point of that advice. It is hinted that Professor Proton may visit him again if he is needed.
In "The Opening Night Excitation", Arthur again appears in his Jedi master robes to advise Sheldon. First he tells Sheldon that he should spend Amy's birthday with her and see the new Star Wars movie another time even though it is the premiere. Second, Sheldon has decided to sleep with Amy and wants to discuss it. Arthur tries to kill himself with his light saber rather than discuss the birds and the bees. Instead, Sheldon is worried that it ws an important night for them and he is afraid he will ruin it. Arthur says that if she is the right woman, everything will be fine. Finally, Arthur shows up wanting to know how their intimacy went; however being Sheldon, he only talks about how much they enjoyed the movie.
Green = Appeared, V = Voiced, C = Cameo, F = Flashback,
M = Mentioned,
Dark Grey = Did not appear,
- The only gang members he doesn't meet before his death are Bernadette, Raj, Howard, Stuart and Emily.
- He and Debbie Wolowitz are the only characters that died that were seen.
- He is the only character seen after he died.
- Chuck Lorre has said he's been pursuing Bob Newhart to appear on one of his shows for a long time. He suggested The Big Bang Theory to Mr. Newhart, who accepted under two conditions: (1) his scenes had to be taped live, and (2) he wanted it to be a semi-recurring role. Lorre was fine with both and later called him with the story of Professor Proton.
- Bob Newhart was nominated for a 2013 Emmy Award for his comedy performance as Professor Proton and won.
- Sheldon purchased a Gino The Neutrino puppet replica on eBay for $20 (including shipping) that he enthusiastically showed to Professor Proton. However, the puppeteer for Gino The Neutrino slept with Arthur’s wife, causing Mr. Jeffries to hate the puppet Gino.
- While sitting on the couch, in Sheldon's spot, in the apartment, Arthur asks Penny if he is in some sort of dream. The TV show Newhart's series finale ended with the entire sitcom being a dream in the mind of Dr. Bob Hartley, Bob Newhart's character from the original The Bob Newhart Show. The series ended with Dr. Hartley waking up in his bed and proceeding to tell his wife from the first show, Emily, about his dream and the crazy people in it, including his beautiful blonde wife. After Emily, a brunette, shuts off the light and tries to go back to sleep, she abruptly turns the light back on and says, "What do you mean she was a blonde?" This one line, in this one scene, may be an homage to one of TV's most famous and surprising story arcs.
- While sitting on the couch, Arthur at one point sat in Sheldon's spot, something that even Sheldon himself didn't mention. He is the only person to this day to have gotten away with sitting in Sheldon's spot. In the season 9 episode The Meemaw Materialization, Sheldon lets his Meemaw, Constance sit in his spot.
- Arthur's comment about giving up smoking may refer to Bob Newhart's movie "Cold Turkey"  where he played a cigarette company executive that promoted smoking.
- Arthur Jeffries despises Bill Nye, claiming that his show was just a rip-off of Professor Proton; he implies that he tried to sue Nye as a result.
- Professor Proton's theme tune is:
- Get your goggles,
- Put your labcoat on,
- here he comes,
- Professor Proton!