Watch: how "5th Beatle" George Martin helped shape the band’s sound

George Martin, the British producer known as the "fifth Beatle," has died at 90.

Before the Beatles were a phenomenon — "more popular than Jesus," as John Lennon famously said — they were a band nobody wanted to sign to a record label. Then they met Martin, who didn't just give them a chance but also shaped the Beatles' sound, writing their unusual orchestral arrangements, and produced all of their albums.

The string quartet on "Yesterday," perhaps the most covered song of all time, was Martin's idea, according to Paul McCartney. In 2001, Martin talked to the Guardian about recording the song:

As they recorded, McCartney wrote on the score: "By Paul McCartney, John Lennon, George Martin, Esq, and Mozart" — in reference to the classical overtones.

When the Beatles recorded "Strawberry Fields Forever," they made two versions. And then Lennon decided the two best versions should be joined together, despite being in different keys and at different tempos. The Rock and Roll Hall of Fame wrote: "Martin recalled of Lennon's reaction: "'Well,' he said, 'you can fix it!' Amazingly, he did."

For "Being for the Benefit of Mr. Kite," Martin said at a Q&A in 2008, he "instructed engineer Geoff Emerick to cut up old tapes of organ music, threw them in the air and onto the floor and then reassembled them at random, running the new sounds concurrent with the song's main organ melody."

In an interview with the Rock and Roll Hall of Fame, Martin described the creative process for writing the orchestral interlude in "A Day in the Life":

"So Paul said, OK, write something. I said what should I write? He said anything… And then he had this idea, look, why don't you start with the orchestra very quiet? Start on their lowest note, end on their highest note, how about that? I knew we'd done something pretty important."

Martin worked with other famous artists as well. His last No. 1 single — of 30 in the US and 23 in the UK — was Elton John's "A Candle in the Wind."

"So sad to hear about Sir George," John wrote in an Instagram post. "It is the end of a wonderful era. I had the privilege to have known him as a friend and work with him as an artist. He was a delightful, brilliant man. We won't see his like again. My deepest condolences to the wonderful Judy and his family."