It's Rutlemania!!! The Rutles are a brilliant parody of The Beatles, born of a remarkable synergy between Eric Idle of Monty Python, Neil Innes of the Bonzo Dog Doo-Dah Band and Lorne Michaels of Saturday Night Live. Originally they were a skit on Eric Idle's 1975 BBC show Rutland Weekend Television, but when Idle hosted SNL and showed the clip, the creative minds at SNL joined Idle and Innes in developing the idea into a feature film - one of the first 'mockumentaries' (and still one of the finest): All You Need Is Cash.
From Wikipedia: "The film is notable for bringing together British and American comic talent in a way that has seldom happened before or since.
All You Need Is Cash is primarily a series of skits and gags that each illustrate a different part of the fictional Rutles story, closely following the chronology of The Beatles' own story. The cohesive glue of the film is the acclaimed soundtrack by Neil Innes, who created 19 more songs for the film, each an affectionate pastiche of a different Beatles song or genre of songs. "
Wikipedia: "The songs written by Innes so cleverly parodied the original source material that he was taken to court by the owners of The Beatles catalogue. Innes had to testify under oath that he had not listened to the songs at all while composing The Rutles songs, but had created them completely originally based on what he remembered various Beatles songs sounding like at different times."