Several recurring and one-shot characters from It's Always Sunny in Philadelphia are extremely popular among fans.
- The McPoyle family for being some of the most fucked up people featured on the show, and making the gang look relatively sane in comparison. Liam is particularly loved for his bizarre lines and delivery, especially showcased in the bloopers where he's able to make the entire cast break. Pappy McPoyle is also particularly loved, despite only appearing in two episodes—it helps that he's played by Guillermo del Toro, who is clearly enjoying every minute of scenery-chewing he gets to do in the role.
- Rickety Cricket, especially once he evolved into the Chew Toy of the series. He toes the line between sympathy and depravity and is a hoot whenever he appears.
- Artemis is adored for being one of the Gang's most likable and easy-going allies who occasionally acts as a Sixth Ranger to their schemes, appears in many of the series' most beloved episodes, and rivals the main cast in quotability.
- The Gang's family members - Bonnie Kelly, Uncle Jack, Mrs. Mac, and Luther - are all loved for their ridiculous personalities and frequent insight into how the Gang became who they are. Even Barbara Reynolds, who died after only a few appearances, enjoys a healthy fandom; Rob, Charlie, and Glenn have stated they regret killing her off so early.
- The Lawyer has gained a following due to being one of the only outsiders who's gotten a handle on how to deal with the Gang's outrageous behavior, trumping them (almost, as per "McPoyle vs. Ponderosa: The Trial of the Century") every time since the entire Gang is legally clueless.
- Ben the soldier, despite not being the brightest bulb on the tree, is liked for being one of the few genuinely nice and good characters on the show who hasn't had his life ruined by The Gang, in part because he's Too Dumb to Fool.
- Z is a quite minor character who's made an impression regardless due to his laid-back and mysterious nature, as well as Chad L. Coleman's hilariously intense delivery (especially seen in his jean shorts speech to the aforementioned Ben). He was even introduced as the sidekick of a character named Duncan, but Duncan was quickly phased out while Z has continued to make appearances.
- Country Mac is a one episode character but quickly became beloved due to being a badass who even the Gang can't help but admire. Many wish he hadn't been killed off at the end of his debut episode.
- Roxy from "Frank's Pretty Woman", thanks to Alanna Ubach's outrageous performance and memorable lines. Some even hope they'll reveal that she didn't really die just so the show has an excuse to bring her back.
- As of "Mac Kills His Dad", the Ponderosas have become this due to somehow being even more of a dysfunctional family than the Reynolds and rivaling the McPoyles in that regard as well.
- Da'Maniac, the insane former pro-wrestler played to perfection by "Rowdy" Roddy Piper and yet another reason to mourn Rowdy's untimely passing.
- Although she only speaks a few words and has about five minutes of screentime, Mac's unnamed dancer partner (played by professional ballerina Kylie Shea) in "Mac Finds his Pride" was an instant hit with viewers thanks to her incredible dance performance in what is almost certainly the most moving moment in the show's entire 13-year history.
- Alexi and Nikki, the two Funny Foreigners who room with Frank and Charlie in the Season 14 premiere.
