First Rock Supergroup?

Probably!
I am in a rockabilly mood, so I am listening to some 1956 tunes by The Johnny Burnette Rock 'n' Roll Trio.
You probably know the story:
Brothers Johnny and Dorsey Burnette grew up in Memphis, where they hung out with a boy named Elvis Presley. They even worked for the Crown Electric Company, where that Presley kid served as a truck driver.
They loved the same kind of music.
Presley began cutting a few records. The Burnette boys were turned down, allegedly for sounding too much like their truck-driving friend. So vocalist/guitarist Johnny and standup bassist Dorsey hooked up with hot-shot lead guitarist Paul Burlison, went to New York, and blazed a glorious, rockin' trail.
The trail ended for Johnny in Clear Lake, Calif., where he died in a drowning accident in 1964. Dorsey continued as a country artist and Burlison retired to run a construction company.
During their brief time together in the late 1950s, nobody could touch these guys. Bill Haley, Roy Orbison, Buddy Holly... they all sound pale compared to these three wild boys.