William “Billy” Cox (born October 16, 1939) is an American bassist, best known for performing with Jimi Hendrix. Cox is the only surviving musician to have regularly played with Hendrix: first with the experimental group that backed Hendrix at Woodstock (informally referred to as “Gypsy Sun and Rainbows”), followed by the trio with drummer Buddy Miles that recorded the live Band of Gypsys album, and, lastly, The Cry of Love Tour trio with Mitch Mitchell back on drums. Cox continues to perform dates with the Band of Gypsys Experience and the Experience Hendrix Tour.

In addition to Hendrix, he has either been a member of the house or touring band or recorded sessions for Sam Cooke, Slim Harpo, Joe Simon, Charlie Daniels, John McLaughlin, Rufus Thomas, Carla Thomas, Lou Rawls, Etta James, Jackie Wilson and Little Richard. Born in Wheeling, West Virginia, Billy Cox was raised in Pittsburgh, Pennsylvania, and attended Schenley High School.