Douglas 'Clay' Cook (born April 20, 1978) is an American songwriter, producer, and musician who is a member of the Zac Brown Band. He plays guitar, slide guitar, Hammond organ, piano, and sings backing vocals (2009–present). He was also a member of The Marshall Tucker Band and Y-O-U. After dropping out of college, he and classmate John Mayer formed the band Lo-Fi Masters. Cook co-wrote several songs with Mayer that appear on Mayer's first two releases, Inside Wants Out and Room for Squares, including "No Such Thing", "Comfortable", "Man on the Side" and "Neon".