Every Guest Star On Young Sheldon Ranked

While fans generally remember "The Big Bang Theory" for the show's witty characters, humorous situations, clever jokes, and its popularisation of the "nerd culture," one thing that made the popular show stand apart was its wide range of cameos and guest stars. From real-life scientists such as Stephen Hawking and Neil deGrasse Tyson, actors and celebrities like Mark Hamill and Charlie Sheen, entrepreneurs and inventors like Bill Gates and Elon Musk, to comic book legends and pop-culture icons like Stan Lee, the award-winning sitcom always packed a star-studded punch.

So, it goes without saying that this secret recipe would be carried on to "The Big Bang Theory's" spin-off/prequel show "Young Sheldon," which focuses on a younger version of fan-favorite character Sheldon Cooper (Jim Parsons), played by Iain Armitage. Much to the satisfaction of fans, the show – in all its five seasons – has delivered many recognizable cameos and guest appearances, some even incorporating the show's late 1980s/early 1990s setting in clever throwbacks to the era. We've gathered a list of 12 of the best guest stars on "Young Sheldon," ranking them down to the most memorable ones.

Richard Kind is recognized by many for his voice roles in several animation films and TV shows, most notably for his emotionally riveting voice work as Bing Bong, Riley's imaginary friend in Pixar's "Inside Out." Kind had guest-starred as Ira Rosenbloom, a furniture store owner and one of Meemaw's (Annie Potts) love interests in 'Young Sheldon" – first introduced in Season 1, Episode 11 ("Demons, Sunday School, and Prime Numbers"). In the episode, Sheldon decides to pursue the faith of Judaism after discovering that his idol Albert Einstein was Jewish. He approaches Ira for a short lesson on the same, though most of Ira's explanations unsurprisingly go over Sheldon's head.

Ira reappears in Season 1, Episode 22 ("Vanilla Ice Cream, Gentleman Callers, and a Dinette Set"), where he and Dr. Sturgis (Wallace Shawn) compete for Meemaw's love in a short-lived love triangle – with Meemaw ultimately choosing Dr. Sturgis over Ira, a rejection that Ira respectfully accepts.

While long-time fans of "The Big Bang Theory" have always known that Sheldon had an intense hatred towards engineers, engineering, and everything to do with the field, it was never really explained why... until now! In "Young Sheldon," Season 5, Episode 7 ("An Introduction to Engineering and a Glob of Hair Gel"), fans finally got to see the origin story of Sheldon's resentment towards engineering. Having appeared on "Fringe," "The Wire," and the "John Wick" series, Lance Reddick guest-starred as Professor Boucher, Sheldon's strict and punctual engineering teacher who, despite Sheldon's best efforts at appeasing him, was always needlessly cruel in his tutoring methods. How cruel, you ask? Constantly tearing apart Sheldon's assignment in front of him without telling him where he was going wrong.

Though he justifies his approach as "tough-love" to Sheldon's father, George (Lance Barber), Professor Boucher causes Sheldon enough distress and frustration for him to develop a life-long disdain towards engineering understandably. At long last, Howard now knows who's to blame for Sheldon constantly teasing and insulting him and his profession! (Though Sheldon admits it's more to do with Howard than engineering).

What made the character of Arthur Jeffries (aka Professor Proton) so memorable on "The Big Bang Theory" was the deadpan humor and stammering comedic delivery that actor Bob Newhart brought to the role, a style of comedy he's most prominently known for. In "The Big Bang Theory," his character Arthur Jeffries played the host Professor Proton in a children's science show that had inspired Sheldon to pursue science from a young age. The now-adult Sheldon (Jim Parsons) was enthusiastic when he finally got a chance to meet Arthur, whom he had always considered his idol. But much to Sheldon's disappointment, it was soon revealed that Arthur actually hated doing his Professor Proton shows.

Making a few cameo appearances as a younger version of his character Arthur Jeffries/Professor Proton in "Young Sheldon," Bob Newhart still manages to bring out the comic misery of the character that's always sadly funny (or funnily sad) to watch! In his first cameo appearance in the series premiere of "Young Sheldon," Arthur (as Professor Proton) teaches the children in his audience how to use potatoes to light a bulb – a subtle foreshadowing/call-back to his first appearance in "The Big Bang Theory" when he uses the same Potato-light-bulb experiment to astonish Penny (Kaley Cuoco).

Back when we all could enjoy an Elon Musk cameo without triggering a heated and controversial debate about it, the entrepreneur and business magnate appeared as a fictitious version of himself at the end of Season 1, Episode 6 ("A Patch, A Modem and a Zantac). By this point, Musk had made cameo appearances as himself in "Iron Man 2," "The Simpsons," "South Park," and even "The Big Bang Theory."

In the episode, a NASA engineer visits Sheldon's class as a guest speaker. Sheldon suggests that the rockets used in NASA's space explorations could be landed instead of letting them drop into the ocean, which can help save millions in US taxpayer dollars. The engineer does not take the 9-year-old Sheldon or his idea seriously, prompting Sheldon to prove him wrong by making the calculations needed to prove his theory. Ultimately, the engineer admits that Sheldon's theory is correct, but NASA does not have the resources to execute it yet. A flashforward ending reveals that SpaceX founder Elon Musk had gotten hold of Sheldon's notebook at some point and used Sheldon's theoretical formulae to execute his SpaceX missions successfully. The chucklesome insinuation that the real-life billionaire owes all his success with SpaceX to a 9-year-old (and fictional) Sheldon Cooper makes this cameo appearance all the more hilarious.

Most recognizable as iconic sitcom character George Costanza from "Seinfeld," Jason Alexander guest stars in "Young Sheldon" as Sheldon's acting teacher Gene Lundy, an unsuccessful actor having settled for a job as the drama coach at Sheldon's high school. First appearing in Season 1, Episode 16 ("Killer Asteroids, Oklahoma and a Frizzy Hair Machine"), Sheldon vows to quit science after losing a competition at the school's science fair, after which he turns to a newfound passion for acting, finding guidance in his acting teacher Gene Lundy. Hilariously, when Sheldon gets cold feet from starring in the titular role of Annie at the school stage play, the middle-aged, bald Lundy steps up in a red dress and orange curly-hair wig to play 11-year-old Annie himself.

Lundy's subsequent misadventures include: playing Satan in a Halloween event sponsored by the church, moonlighting as a real estate agent, and making a workout tape with David Hasselhoff. It's always a treat to watch Jason Alexander in anything he's in, and his appearances in "Young Sheldon," though infrequent, have always managed to entertain.

At the top of our list, we have one-half of television's cutest couple, Shamy! To those who haven't watched "The Big Bang Theory," "Shamy" was a nickname coined by Penny (Kaley Cuoco) for Sheldon and Amy – much to Sheldon's distaste for the name.

Mayim Bialik reprises her role in "Young Sheldon" as Amy Farrah Fowler, Sheldon's wife and mother of his children. First appearing in a voice cameo at the end of Season 4, Episode 1 ("Graduation"), Amy intrudes in on Sheldon's narration about the decision of naming their son "Leonard Cooper," after the "Star Trek" actor (and Sheldon's hero) Leonard Nimoy. Her appearance was a pleasant surprise for fans, who were pleased by the revelation that the couple had a son after the finale of "The Big Bang Theory."

Sheldon invites Amy to join the narration again at the beginning of Season 5, Episode 16 ("A Suitcase Full of Cash and a Yellow Clown Car"), as they both have an amusing banter on the topic of relationships and physical intimacy – building on the running gag in "The Big Bang Theory" of Sheldon's aloofness towards Amy's desire for intimacy. Despite the quirks of their relationship, it was heart-warming for loyal fans to see the endearing "Shamy" still going strong years after we bid goodbye to them in "The Big Bang Theory" series finale.