"Billy Preston, 59; Dazzling, Troubled Keyboardist Known as the `Fifth Beatle'"
Like it or not, this is what he'll be most remembered for doing.
Beatle George brought Billy into the studio while the Fabs were struggling through the beginning of their breakup period, hoping his presence would add a spark. I'd say the goal was achieved!
The Wikipedia page for Preston has this information about his "Beatles phase":
"...he was probably best known for his work with the Beatles. He played on their 1970 album Let It Be and on the songs 'I Want You (She's So Heavy)' and 'Something', from 1969's Abbey Road. Signed to their Apple label, in 1969, Preston released the album That's the Way God Planned It and a single of the same name (produced by George Harrison). His relationship with Harrison continued after the break up of The Beatles; he was the first artist to record 'My Sweet Lord' (the single flopped), and he was on several of George's 70's solo albums..."