Rob McElhenney (b. 1977, Philadelphia, Pennsylvania) is an American film and television actor best known for his role as Mac on the FX TV series It's Always Sunny in Philadelphia. He is also credited as creator, developer and executive producer of the show, which has also provided McElhenney with writing and directing credits on various episodes.
McElhenney made his film debut with a bit part in The Devil's Own and followed that up with bit parts in A Civil Action and Wonder Boys. He later had more substantial parts in Latter Days and The Tollbooth.
He was still waiting tables between acting assignments in 2004, when his manager and agent presented McElhenney's idea for a "Seinfeld on crack" sitcom to the FX cable network, which received it warmly. McElhenney said that 50 weeks of each year are consumed by acting, producing, and writing for the show, but he did find time to appear in the third season of the television show Lost as Aldo in the seventh episode, "Not in Portland". This was as a result of McElhenney meeting Lost co-creator and executive producer Damon Lindelof. Lindelof is a fan of It's Always Sunny in Philadelphia, and offered to give Rob a small role in an episode.
McElhenney is a 1995 graduate of St. Joseph's Preparatory School.
In an interview with 93.3 WMMR morning show Preston and Steve, McElhenney announced that he and Sunny costar Kaitlin Olson have been dating for over a year. As of December 2007 McElhenney and Olson are engaged.