Glenn Franklin Howerton III (born April 13, 1976) is an American actor, writer and producer. 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... Wikipedia