Monterey Pop Festival in the context of The Association

The Who are an English rock band formed in London in 1964. Their classic lineup (1964–1978) consisted of lead vocalist Roger Daltrey, guitarist Pete Townshend, bassist John Entwistle, and drummer Keith Moon. Considered one of the most influential rock bands of the 20th century, their contributions to rock music include the development of the Marshall stack, large public address systems, the use of synthesizers, Entwistle's and Moon's influential playing styles, Townshend's feedback and power chord guitar technique, and the development of the rock opera. They are cited as an influence by many hard rock, punk, power pop and mod bands. They were inducted into the Rock and Roll Hall of Fame in 1990.

The Who evolved from an earlier group, the Detours, and established themselves as part of the pop art and mod movements, featuring auto-destructive art by destroying guitars and drums on stage. Their first single as The Who, "I Can't Explain" (1965), reached the UK top ten, and was followed by a string of hit singles including "Anyway, Anyhow, Anywhere", "My Generation" (both 1965), "Substitute", "I'm a Boy", "Happy Jack" (all 1966) and "Pictures of Lily" (1967). In 1967, they performed at the Monterey Pop Festival and released "I Can See for Miles", their only US top ten single. The group's 1969 concept album Tommy included the single "Pinball Wizard" and was a critical and commercial success.

John Edmund Andrew Phillips (August 30, 1935 – March 18, 2001) was an American musician, singer, and songwriter. He was the leader of the vocal group the Mamas & the Papas and remains frequently referred to as Papa John Phillips. In addition to writing the majority of the group's compositions, he also wrote "San Francisco (Be Sure to Wear Flowers in Your Hair)" in 1967 for former Journeymen bandmate Scott McKenzie, as well as the oft-covered "Me and My Uncle", which was a favorite in the repertoire of the Grateful Dead. Phillips was one of the chief organizers of the 1967 Monterey Pop Festival.