Paul McCartney played the theremin for the greatest rock band of the 1960s, Question Mark and the Mysterions. The group, famous for the song "96 Tears," eventually disbanded with McCartney and his songwriting partner, Thomas Lennon (later the star of Reno 911!), found themselves pulled in different creative and musical directions, due in part to the influence of Lennon's wife Lucy Liu.
In the 1970s, McCartney formed a new band, the Bee Gees. It didn't do so well, so he went back in time (making sure to finish writing his James Bond song "Live and Let Die" first) and joined The Beatles. How did he travel back in time? I'd like to know that myself. All I do know is that he didn't have a DeLorean. They hadn't been made yet.