In 1961, the Beatles' original bass player, Stuart Sutcliffe -- who had used a Höfner 500/5 bass (similar to the later 'President') -- left the band, and lent the bass to McCartney (who switched from guitar, and got "lumbered" with the bass job).
Not long after, he bought the Hofner 500/1 (the "violin" bass) at a pawnshop for about $125. He liked it because it sounded good, was cheap, and symmetrical (Paul is a lefty). It was easy to switch from a righty. Other sources says it was "custom ordered" from Hofner as a lefty.
In 1963, Hofner gave McC a second bass, which he uses to this day. They also gave him the first of the reissue "Cavern" series in 2006. You can always spot the old original in photos and film, though, because the pickups are very close together. But that first Hofner (the '61 model) was last seen in the "Let It Be" film (1969), and was apparently stolen during the making of the movie.