The Role of Mac on ‘It’s Always Sunny in Philadelphia’ Was Originally Supposed to Go to This Actor Instead of Rob McElhenney

It may be hard to imagine anyone other than Rob Mac cultivating mass, denouncing science, offering ocular patdowns and performing emotional interpretive dances as It’s Always Sunny in Philadelphia’s Ronald “Mac” McDonald, but the actor’s now career-defining role wasn’t always a sure thing.

During the early days of the show, Mac — then called “Rob,” per The Always Sunny Podcast — was portrayed by David Hornsby, who would later go on to play Rickety Cricket.

“McElhenney’s girlfriend at the time, actress Jordan Reid, was playing Sweet Dee, the female foil to the three fellas, and Mac was being played by… not McElhenney,” author Kimberly Potts recalls in her new book, It’s (Almost) Always Sunny in Philadelphia: How Three Friends Spent $200 to Create the Longest-Running Live-Action Sitcom in History and Help Build a Network. 

Even though Mac “had his hands full with writing, directing and producing the film, overseeing the whole enterprise, and holding one of the cameras,” as Potts put it, the multi-hyphenate still found time to step in for Hornsby during shoots when he was absent, ultimately taking over his post. 

This revelation isn’t exclusive to the new book. Back in 2022, Mac got candid about not only replacing Hornsby, but also his hesitancy to take on a starring role in his own show, telling Charlie Day and Glenn Howerton that he “never considered” himself to be “a super funny performer” prior to Always Sunny. 

“I always thought that I could write really funny stuff,” he recalled to his co-stars during an episode of the Always Sunny Podcast. “I didn’t think I could pull this off, but I feel like maybe the two of you could make this scene really funny, and then sure enough you did. So then my thought was, why not just populate this show with really funny people that can make this dark material really funny.”

Considering the events of the past 16 seasons (and counting), he definitely wasn’t wrong.