Glenn Franklin Howerton is an American actor and filmmaker. He is best known for his roles as Dennis Reynolds in It's Always Sunny in Philadelphia, for which he is also a writer and executive producer, and Jack Griffin in A.P. Bio, as well as the lead role in the short-lived sitcom That '80s Show.
Howerton was going to study Aerospace Engineering at Auburn University before deciding to attend Juilliard, where he graduated with a B.F.A. in the Actor Training Program. He is a fairly talented vocal mimic and acquits easily to impersonating various dialects, a skill he developed during his "military brat" childhood which require constant moving to different areas and countries.