Craig Gruber, a longtime former collaborator of Ronnie James Dio's, died yesterday after a bout with prostate cancer. He was 63.

Gruber most memorably appeared on 1975's Ritchie Blackmore's Rainbow, a No. 11 UK smash, after a two-album stint with Elf – which, like the earliest editions of Rainbow, featured Dio as frontman. Elf's Gary Driscoll, David Feinstein and Mickey Lee Soule rounded out the sessions players for Ritchie Blackmore's first studio project after leaving Deep Purple.

Elf had served as opening act during Purple's Stormbringer tour, where Blackmore and Dio struck up a friendship. Years later, Gruber remembered how quickly one band morphed into the other. "Don't say anything and at the end of the tour, Elf is no more, and we're forming a band with Ritchie Blackmore," Gruber remembered Dio saying before the tour was even over. "I'm, like, 'Holy s---, dude.' That was actually the beginning of Rainbow."

Gruber had been part of 1975's Trying to Burn the Sun and 1974's L.A. 59 albums with Elf, taking over after Dio handled bass duties on the band's 1972 self-titled debut. Gruber later worked with Dio in the earliest sessions for the singer's first album as Ozzy Osbourne's successor in Black Sabbath, though Geezer Butler ultimately returned in time to complete what would become 1980's Heaven and Hell.

An '80s-era reunion with former Elf bandmate Driscoll, Bible Black, produced an eponymous debut LP and a follow-up, Ground Zero, before Driscoll's murder in 1987. Gruber subsequently played on Gary Moore's 1984 live album We Want Moore, a Top 40 U.K. hit recorded during the tour in support of 1983's Victims of the Future. There was also a Deep Purple connection there: Drummer Ian Paice sat in on seven tracks from We Want Moore.

See Other Rockers We've Lost in 2015

More From US 103.1 FM