Bill Black was 9 years older than Elvis. Bill was very instrumental in getting Elvis over his initial stage fright and told him to move around to entertain the audience. At many points in 1954 when they first started, Bill would MC the Elvis shows and "egg on" Elvis to "do more".
Here is Elvis on board the USS Hancock - April 1956. Bill Black almost got "fired" for stealing the show. Watch at the 2 minute mark. Bill rides and slaps his Bass with both hands. By this time Elvis was under the management of Col. Tom Parker, who scolded and almost fired Bill for stealing the show because of this antic. Elvis intervened and kept Bill on.
By the time Elvis went to the Army 2 years later, Bill Black had started using a Fender Precision Bass and eventually started his own group - The Bill Black Combo. They mainly did Instrumentals.
The Bass in this video aboard the USS Hancock is now owned by Paul McCartney of the Beatles. At some point between 1956 and 1966 when Bill Black died, the Bass was painted Gold.
The best history I can find about Bill Black is here - http://www.rockabillyhall.com/BillBlack.html