Which is the only act that played Monterey in 1967, Woodstock in 1969, and Live Aid in 1985?

"The Who" are an English rock band formed in London in 1964. Their classic line-up consisted of lead singer Roger Daltrey, guitarist and singer Pete Townshend, bass guitarist John Entwistle and drummer Keith Moon. They are considered one of the most influential rock bands of the 20th century, selling over 100 million records worldwide.

The Monterey International Pop Music Festival was a three-day concert event held June 16 to June 18, 1967, at the Monterey County Fairgrounds in Monterey, California, USA, and it became an inspiration and a template for future music festivals. "The Who's" appearance at Monterey gave them recognition in the US, and "Happy Jack" reached the top 30.

Woodstock was a music festival held August 15–18, 1969, on Max Yasgur's dairy farm in Bethel, New York, USA. The festival has become widely regarded as a pivotal moment in popular music history. "The Who" were scheduled to appear on Saturday night, 16 August, but the festival ran late and they did not take to the stage until 5 am on Sunday; they played most of their rock opera, "Tommy."

Live Aid was a dual-venue benefit concert held on Saturday 13 July 1985 organized to raise funds for relief of Ethiopian famine. The event was held simultaneously at Wembley Stadium in London, England, and John F. Kennedy Stadium in Philadelphia, Pennsylvania, USA. This was "The Who's" first appearance since their 1982 "farewell" tour.

As of October 2019, "The Who" are still touring and releasing albums.