William Cox (born October 18, 1941) 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.

Cox met Jimi Hendrix when they were serving in the Army at Fort Campbell, Kentucky, in 1961. While using the bathroom at Service Club No. 1 during a sudden rainstorm, he heard guitar playing inside. Impressed with what he heard, he introduced himself, told Hendrix he played bass, and they were jamming soon after. They became, and remained, fast friends. They left the military around the same time and they played clubs around Clarksville, Tennessee, finally moving to Nashville. They formed a group called the King Kasuals. They played at Nashville clubs, mostly the Del Morocco, and occasional outlying gigs in the southeast, once as far north as Indianapolis playing what was called the “Chitlin’ Circuit“. Cox and Hendrix also played in the backing band for Marion James around this time.