Which band did Tony Iommi briefly join in December 1968?

Tony Iommi briefly joined Jethro Tull in December 1968.

At the time, Iommi was the guitarist in Earth, the Birmingham group that would soon become Black Sabbath. Jethro Tull recruited him after he impressed the band during a Birmingham performance. His stay was extremely brief: he played only two engagements before returning to Earth.

One of those appearances was at The Rolling Stones Rock and Roll Circus, filmed on 11 December 1968. Jethro Tull performed “A Song for Jeffrey,” but the performance was largely mimed to a studio recording; Ian Anderson’s vocals and flute were live, while the recording featured Mick Abrahams on guitar.

Iommi left because he felt more connected to his old Birmingham band and disliked Jethro Tull’s more leader-centered direction. He rejoined Earth in November 1968, and the group later adopted the name Black Sabbath. Martin Barre subsequently became Jethro Tull’s long-term guitarist.