Which 1970 Bath Festival headliner inspired Michael Eavis to start Glastonbury?

The 1970 Bath Festival headliner who inspired Michael Eavis to start Glastonbury was Led Zeppelin.

Eavis attended the Bath Festival of Blues and Progressive Music at the Bath and West Showground in Somerset in June 1970. Led Zeppelin headlined the event, performing a major three-hour set as the sun went down. Seeing the scale and atmosphere of that open-air concert encouraged Eavis to stage his own festival later that year at Worthy Farm in Pilton.

That first event, held on 19 September 1970, was called the Pilton Pop, Blues & Folk Festival and attracted about 1,500 people. It was not yet the large annual Glastonbury known today. The original planned headline acts, The Kinks and Wayne Fontana and the Mindbenders, were replaced at short notice by Tyrannosaurus Rex, later known as T. Rex. Pink Floyd also performed at Bath, which makes them a tempting but incorrect answer to this question; the specific act credited with inspiring Eavis was Led Zeppelin.