Billy Cox holds a unique position in the life of Jimi Hendrix. Cox knew and played in bands with Hendrix before he became famous, and after. Billy first met Hendrix in the early part of the Sixties, when they were both in the Army. Cox, a bass player, teamed with Hendrix in an R & B band called the King Casuals. 
They re-united musically in 1969, when Hendrix called on Cox to play bass in the experimental funk band the Band of Gypsys. 
Billy Cox played at Woodstock with Hendrix's Gypsy Sun and Rainbows, and toured with Hendrix (with Mitch Mitchell on drums) for most of 1970 on the Cry of Love tour.
Cox lives in Nashville TN. where he remains active in music, and acts as an ambassador for Jimi Hendrix, his music and philosophy. 

For more a lot more great information on Billy Cox, visit David's Tribute to Jimi.