Glenn Franklin Howerton III is an American actor. He is best known for playing Dennis Reynolds on the long-running sitcom It's Always Sunny in Philadelphia (2005–present) on FX/FXX, a series he co-developed with Rob McElhenney, and on which he serves as an executive producer and writer. On film, he is best known for his portrayal of Jim Balsillie in the Canadian film BlackBerry (2023), for which he received widespread critical acclaim. Wikipedia