Nicholls was originally brought in as a second guitarist when Black Sabbath doubted whether they would even continue under that name. Nicholls then switched to bass when Geezer Butler left briefly, and then became the band's keyboardist upon Butler's return and the decision to keep the Sabbath name. Nicholls' first appearance on a Black Sabbath album was on 1980's Heaven and Hell, and was credited as keyboardist on every Sabbath release from that time until 13, although he was not an official member until 1986. He remained an official member until 1991, then regained member status from 1993 to 1996. He was an unofficial member once again since the reunion with Ozzy Osbourne in 1997. Although his main role with Sabbath has been on the keyboard Nicholls also played some rhythm guitar on the