20 celebrities who have appeared on ‘It’s Always Sunny in Philadelphia’

Before Lance Barber was known to many as Sheldon Cooper’s dad on Young Sheldon, Lance Barber was a less-than-stellar dad father on Sunny, a former classmate of Sweet Dee and Dennis known as Bill Ponderosa.

Jimmi Simpson gained acclaim for his role as The Man in Black on HBO’s million-dollar series Westworld, but Sunny fans will always know him as one-half of the creepy McPoyle brothers.

Once in a while, fans are introduced to random family members, and that includes Mac’s cousin, played by American Pie’s Seann William Scott.

Mindy Kaling of The Office (and The Mindy Project) appeared on the 13th season premiere as Cindy, a woman of color whose purpose was to better the group. Of course, there’s no bettering them, which is why fans love them.

Known for his role on The Wire, Chad L. Coleman has appeared in a handful of Sunny episodes as Z, including "Dee Gives Birth," in which he was one of the candidates for the father of Sweet Dee's baby.

When the gang got stranded in the woods, Tom Sizemore was there as the creepiest trucker to pick them up.

Dax Shepard showed up in a 2015 episode when Mac and Charlie found themselves in the depths of a cult.

Known to Sunny fans as Dennis' ex-wife with the dead tooth who transformed into a cat (sounds wild to non-Sunny watchers, for sure), Catherine Reitman not only starred in the Netflix series Workin' Moms but is also the daughter of late director Ivan Reitman.

After working together on Pacific Rim, Guillermo del Toro guest starred on not one but two episodes as Pappy McPoyle, including one of the most chaotically hysterical, "McPoyle vs. Ponderosa: The Trial of the Century."

When Sunny decided to explore race relations in America and found themselves in an episode that was a musical version of Quantum Leap, there was no one else better to play Scott Bakula than Scott Bakula.

The same year the world bid farewell to The Office, Oscar Nuñez went from an accountant to a manager on the episode “The Gang Tries Desperately to Win an Award.”

Mary Lynn Rajskub does her thing as a comedian and was one of the stars of Fox’s 24, but to Sunny fans, she’ll always be someone they want to throw salt at as she’s a recurring character, the annoying cousin Gail the Snail.

"The Gang Goes on Family Fight" is a fan-favorite in which Keegan-Michael Key plays the host of a Family Feud-style show that, like most people on the show, cannot stand the antics of the core cast.

The Kids in the Hall alum has appeared as Principal MacIntyre a few times since 2010, with the best scene being when he had to interact with Charlie, applying for a job at his school with a resume that was just a photo of Caitlyn Jenner when she was an Olympian.

Bryan Cranston (as well as his Breaking Bad co-star Aaron Paul) poked fun at the idea of celebrities making their own alcohol brands, only for Charlie Day, Glenn Howerton, and Rob McElhenney to turn around and announce their own after “Celebrity Booze: The Ultimate Cash Grab" aired.

Sandy Martin has been an important part of the Sunny puzzle since pretty much the start as Mac’s very rough, around-the-edge mother, but before that, she was Napoleon Dynamite’s grandma.

Sunny has had its fair share of musicians, from Josh Groban to Matchbox Twenty’s Rob Thomas and Puff Daddy, a.k.a P. Diddy, a.k.a Sean Combs, in “Charlie's Mom Has Cancer.”

Fans of The Boys might be surprised to know that P.J. Byrne was on Sunny way back in 2009 on "The Gang Exploits the Mortgage Crisis."

Reginald VelJohnson is forever a man of the law as he’s played an officer in both Die Hard and Family Matters, as well as a judge on It’s Always Sunny.

Lynne Marie Stewart has been working in Hollywood since 1971, appearing in the likes of American Graffiti, Pee-Wee's Big Adventure, and in recent years, Bridesmaids with It's Always Sunny being her most recent and reoccurring project where she plays Charlie's mother, Bonnie.