I voted George Martin. Seems so obvious really to me. And most of you from the vote results. The End says he was never in the band, but, he made musical contributions as though he were in the band. Where would a lot of The Beatle's songs be without Martin's fantastic orchestral scores? And the music he wrote for Yellow Submarine on the soundtrack album is really nice too, while we're on the subject of George Martin.
Sir George did a good job...and he was paid... oh, I love the keyboards parts he played on stage with the guys during the Beatlemania era... and his harmonies too, of course.
In music, the producer always takes part in the work in studio but a band is more than the studio work.
Aren't the guys a foursome? I knew them as the Fab FOUR. Let's count: John (1), Paul (2), George (3) and,...and,... yeah,and Ringo(4): 1+1+1+1=4 Where's the 5th one?