"The Pinheads" was a band consisting of Marty McFly, Paul, Lee, and Bobby. The Pinheads were portrayed by Michael J. Fox (guitar), Paul Hanson (bass guitar, who was Fox's guitar coach for the movie and actually played Michael's guitar solo in this scene), Lee Brownfield and Robert DeLapp. Their characters weren't named in the credits of the film, but in the comic "Back to the Future: Who Is Marty McFly?" they were named Paul, Lee, and Bobby after their actors.

The band was formed when the three original members, Marty, Lee, and Paul, were in elementary school.

In 1979, Douglas J. Needles moved to Hill Valley from Bakersville, and bought his way into the band with his his mother's money. Since Doug couldn't play his guitar and he was a showoff, Lee and Paul told Marty they didn't want him in the band. Doug overheard this and started his own band. This furthered Doug's grudge against Marty.

Bobby joined the band in 1985, after Marty got his truck, when the four of them went on a camping trip. In the original timeline, when Marty didn't own the truck, they took a bus to the campsite instead.

More Info: backtothefuture.wikia.com