Answer:
Probably the most famous people the Beatles met were each other!
Obviously, the Beatles met many well known people of the 1960s; meeting Elvis (who'd been a hero for the band members) was a big thing for all of them. They also met (without quite realising who it was) the British Prime Minister, Harold Wilson. Early in their career in the USA, they met Mohammed Ali.
They also appeared as guest stars on the Morecambe and Wise show.