William Clay Matthews, Jr. (born March 15, 1956 in Palo Alto, California) is a former American football linebacker who played for the Cleveland Browns and the Atlanta Falcons. He played 19 seasons and 278 games in the NFL (third most in NFL history). Matthews was drafted by the Browns out of USC with the 12th pick in the first round of the 1978 NFL Draft. Clay was a four time Pro Bowler for Cleveland.

Clay Matthews' father (Clay Matthews, Sr.) and brother (Bruce Matthews, who also played at USC) were also NFL players. Two of his sons joined the football team at USC: Kyle was a walk-on safety (2000-03) and Clay III is a walk-on linebacker (2005- ).

As of 2005, Matthews resides in the Los Angeles area and is a high school football coach. He was inducted into the USC Athletic Hall of Fame in 2005, along with his brother Bruce.