behind the music, it would have to be George Martin the producer. Many knew the name because it was on every album. He was credited with being the "5th Beatle". I liked to call him the "2nd George".
Martin had an ear for the times. He sped up the tempo on "Please Please Me", one of the Beatle's earliest hits. Against Paul McCartney's wishes, he added a string quartet to "Yesterday". He kept the guitar feedback in "I Feel Fine" and made it sound like it belonged in the song. Martin himself played a piano riff in the Rubber Soul song "In My Life". He produced the groundbreaking "Sargent Pepper's Lonely Hearts Club Band" album.
He is perhaps due a lot more of the credit for the Beatles success than he received, but he was fine with that. The Las Vegas Cirque du Soleil Beatles tribute "Love" was a collaboration of Martin and his son Giles.
Sir George Martin died in his sleep on March 8th. He was 90.