Craig Gruber, famous in the rock community for his roles as bassist for two Ronnie James Dio groups, has died. He passed away from complications of prostate cancer on Tuesday. Gruber was 63 years old.

In the early 1970s, Ronnie James Dio was the bassist and vocalist for a band he founded called the Electric Elves. As the band progressed through the early part of the decade, they changed their name to Elf, and enlisted the help of Craig Gruber on bass. With Ronnie James Dio focusing on lead vocals, Gruber formed the backbone of the band’s rhythm section. He was featured on the group’s 1974 and 1975 albums.

Elf was such a solid group of musicians when they performed together that almost everyone in the group was asked to form a new band called Rainbow. Ritchie Blackmore from Deep Purple asked members of Elf, including Dio and Gruber, to join him on Rainbow’s first album.

Although he would only perform on Rainbow’s debut album, Gruber wasn’t out of work by any means. He has performed with famous guitarists such as Gary Moore, and had his own projects Bible Black (featuring Rainbow’s Gary Driscoll), Raven Lord and Zvekan.

Before his death, Gruber was building a line of basses made specifically for soloing. He had also talked about doing an Elf reunion, although the deaths of Driscoll and Dio in previous years would make that reunion incomplete.

Take a listen to some of Gruber’s best-known work below: