Before the Beatles, John Lennon, Paul McCartney, and George Harrison were originally members of which band?
And the answer: The Quarrymen.

The Quarrymen name came from a line in the school song of the band members' school, Quarry Bank High School in Liverpool. Founded by John Lennon, the Quarrymen played at parties and school dances. In 1960, the group changed their name to the Silver Beetles, and eventually settled on the simpler name, "the Beatles."
For one of the most famous bands of all time, if not the most famous, the Beatles' conception was a humble one. Lennon, driven by his love for rock-n'-roll, gathered around him a group of friends to create a bit of skiffle music: a highly animated, heavily rhythmic variant on American folk and country music. The group's beginnings were unsure, and members would filter in and out depending on their availability for gigs. For weeks, it seemed like the Quarrymen wouldn't go much of anywhere.
However, history had other plans. Lennon found allies in two new members: George Harrison and Paul McCartney. Playing around Liverpool, the group picked up a steady but meager following. New members continued to join and depart, and the group changed their name to the Silver Beetles, and later, just the Beatles. Very soon after that – just a year after the conception of the Quarrymen – the Beatles were making their first recordings in Hamburg. From there, it only went up.
Learn more about the nascent, transformative Beatles here.
