It's Always Sunny: The 5 Most Memorable Guest Stars (& 5 We Forgot About)

It's Always Sunny In Philadelphia, the sitcom which has been on the air for 13 seasons, has had some funny (and some forgettable) guest stars.

Where there are popular TV shows, there are celebrity guest stars. After any show has been on the air for a while and gained a sizeable fan following, famous faces begin popping up, and It’s Always Sunny in Philadelphia is no different. Having been on the air for 13 seasons and become one of the defining cult sitcoms of the 21st century, It’s Always Sunny has attracted some pretty big names for one-off appearances, and they don’t go easy on them – they get them to play characters that are just as weird as we expect from this show.

RELATED: It's Always Sunny: 10 Ways The Gang Has Changed Since Season 1

So, here are the 5 most memorable guest stars from It’s Always Sunny and 5 that we forgot about.

10 Most Memorable: Seann William Scott As Country Mac

Seann William Scott might be best known for playing Stifler in the American Pie movies, but he makes quite an impact in the Always Sunny season 9 episode “Mac Day,” in which he plays Country Mac, Mac’s cousin who lives in the country. What makes Country Mac hilarious is that all of his characteristics are better versions of Mac’s, and he can do all the things Mac claims he can do: he’s genuinely tough, his ocular pat-downs actually work, he’s open about his homosexuality (this was before Mac was, too), and his religious views aren’t defiantly tied to the literal meaning of the Bible.

9 Forgot About: Dax Shepard As Jojo

The season 10 finale “Ass Kickers United: Mac and Charlie Join a Cult” is one of the show’s weakest episodes altogether. It’s kind of fun that the producers got Dax Shepard to play a weirdo that followed the cult that Dennis created to get Mac to stop eating his cookies, but his character doesn’t amount to much. He’s just sort of there for the whole episode and then, at the conclusion, he dies in the second fire to burn down Mac and Dennis’ apartment. However, it was a nice touch to show him in a higher realm of existence over the end credits, riding the space turtle whose dream we all apparently live in.

8 Most Memorable: Keegan-Michael Key As Grant Anderson

In the season 10 episode “The Gang Goes on Family Fight,” Keegan-Michael Key plays Grant Anderson, the host of Family Fight, the fictional game show that the Gang appears on. Key does a fantastic job of playing the over-the-top, excitable line delivery of game show hosts, and as he gets angrier and angrier at the Gang throughout the episode, we see him struggle to hide his rage from the viewers until he eventually blows his lid. It’s a subtle performance that rises slowly throughout the half-hour, so there’s more to this appearance than just the novelty that it’s Keegan-Michael Key in It’s Always Sunny.

7 Forgot About: Alexandra Daddario As Ruby Taft

In the season 8 episode “Charlie and Dee Find Love,” Dennis thinks that Charlie and Dee’s new beaus are luring them into a She’s All That/Dangerous Liaisons type situation. And while Dee’s new boyfriend turns out to be doing just that, Charlie’s new girlfriend – Ruby Taft, played by True Detective star Alexandra Daddario – actually does care about him. But then Charlie turns out to be using her to make the Waitress jealous. It’s a fun twist, and a neat way to end the story, but ultimately, Daddario doesn’t make much of an impression, since her character was just a pawn in Charlie’s game.

6 Most Memorable: Josh Groban As Himself

Way back in “Mac’s Mom Burns Her House Down,” Dee tried to attend a Josh Groban concert before Frank made her too sick to go in an attempt to get her to look after him, saying that the young crooner “likes his ladies to pop.” The joke was paid off in a fantastic way years later in the show’s 100th episode “The Gang Saves the Day.”

RELATED: Dee Reynolds: 10 Funniest Quotes From It's Always Sunny's Golden Goddess

During Dee’s dream sequence, she marries Groban and he appears as himself, confirming that he does, in fact, like his ladies to pop. Then, he sings Dee a song about the normal size of her feet and how she doesn’t look like a bird.

5 Forgot About: Mindy Kaling As Cindy

Even though Mindy Kaling appeared in the most recent season of It’s Always Sunny, she didn’t make a big enough impact to be truly memorable. In the season 13 premiere “The Gang Makes Paddy’s Great Again,” Kaling plays Cindy, the forward-thinking, progressive-minded liberal brought in supposedly to replace Dennis when it was unclear if he’d return. She tries to get the Gang to move on from Dennis, but simply can’t. Unfortunately for Kaling, although she does a fine job of playing the character, the whole point of her being there is that no one can replace Dennis and anyone who does will be instantly forgettable.

4 Most Memorable: Sean Combs As Dr. Jinx

In the season 8 episode “Charlie’s Mom Has Cancer,” Sean Combs plays Dr. Jinx, the church gardener and funk musician who pretends to be a doctor in Bonnie’s cancer scam. Just like in his other comedic performances, particularly in Get Him to the Greek, Combs is hysterical in the role. He uses a cleaning chemical on Mac’s rash and lays down a bassline to bring Dennis’ emotions back, but his finest moment in this episode is his rendition of “Give Up the Funk” at the fundraiser where he tweaks the lyrics slightly to say, “We’re gonna turn this cancer out!”

3 Forgot About: Tom Sizemore As A Trucker

A lot of fans forget that Tom Sizemore was in It’s Always Sunny. In fact, not many viewers even recognized him. But his turn in the season 6 episode “The Gang Gets Stranded in the Woods” is hilarious. He plays the trucker with whom Charlie and Dennis hitch a ride to Atlantic City, where they meet Mac’s hero Chase Utley and spend the night drinking with him. Sizemore plays the trucker as a total pervert who mistakes Charlie and Dennis for a pair of high-class hookers and wants to take them to a motel room, despite their insistence that they’re just hitchhiking.

2 Most Memorable: Jason Sudeikis As Schmitty

In the episode “The Gang Gets a New Member,” Charlie is kicked out of the Gang and replaced by Schmitty, their old buddy who was kicked out when Charlie butted heads with him. When Dennis, Mac, and Frank choose Schmitty over Charlie the second time, things seem great at first.

RELATED: It's Always Sunny In Philadelphia: Every Supporting Character, Ranked

However, he starts to question Dennis’ leadership and the Gang’s weird ceremonies, so he gets pushed out of a moving car. Jason Sudeikis – Charlie Day’s co-star from the Horrible Bosses movies – does a hysterical job of being both the straight man to the Gang’s antics and playing Schmitty as a genuinely fun guy.

1 Forgot About: Sinbad As Himself

It’s easy to forget that Sinbad once appeared in It’s Always Sunny, because it was in one of the show’s early seasons – the fourth one – and a twist at the end reveals that he was never actually there. In season 4’s “Dennis Reynolds: An Erotic Life,” Dennis goes to rehab and gets tormented by Sinbad and Matchbox Twenty’s Rob Thomas. Sinbad makes Dennis his “b***h,” but Dennis later realizes that he imagined the whole thing and the rehab he was in was actually an auto repair shop. Sinbad is hilarious in the episode, but the episode itself isn’t wholly memorable.

NEXT: It's Always Sunny in Philadelphia Star Finally Plays Catch With Chase Utley

Next The Avengers: Every Main Character, Ranked By Intelligence