William Clay Matthews III (born May 14, 1986) is a former American football outside linebacker who played 11 seasons in the National Football League. The six-time Pro Bowl selection and two-time All-Pro played primarily with the Green Bay Packers.

After attending Agoura High School in Agoura Hills, California, Matthews was a walk-on student athlete at the University of Southern California for the USC Trojans football team under head coach Pete Carroll. At USC, Matthews was a standout special-teams player, winning three consecutive Special Teams Player of the Year awards from 2006 to 2008. He also played reserve outside linebacker during those years before moving into a starting role his senior season. During his college career, he was a part of three Pac-10 Championship teams.