Technically there were only 4 Beatles that became famous. John
Lennon, Paul McCartney, George Harrison, and Ringo Starr. However
Stuart Sutcliffe and Pete Best also played in the band for a little
while.
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At various times, keyboardist Billy Preston, arranger George
Martin or manager Brian Eptein have all been referred to as "the
fifth Beatle". Also, a NYC DJ "Murry the K" took to calling himself
this when the Beatles came to the US in 1964.
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As for all Beatles recordings, George Martin (the fifth Beatle)
was the producer.