George Martin - the man who signed The Beatles to a recording contract in 1962 and produced the vast majority of their hits - died last night, March 7, at home. He was 90. Although he always worked behind the scenes, Martin's influence on the Fab Four's sound was immense. That's why Paul McCartney reacted to the news by saying, "If anyone earned the title of the fifth Beatle it was George."

To celebrate his life and the others who have been considered honorary members of the group, we put together a list of people considered the "fifth Beatle."

1. Stuart Sutcliffe or Pete Best

Unlike the others mentioned in this list, Stuart Sutcliffe and Pete best were actually members of The Beatles. Sutcliffe played bass and Best banged the drums back when the group was a five-piece gigging in Hamburg, Germany.

When the others returned to Liverpool, Sutcliffe stayed in Germany and worked on his painting. He tragically died of a brain hemorrhage on April 10, 1962. That same year, Pete Best was fired from the group and replaced with Ringo Starr because the group and George Martin found Best's chops underwhelming.

Check out the band recalling Best's exit and Ringo's entrance in this clip from The Beatles Anthology:

2. Andy White and Jimmy Nicol

The drummer saga would lead to two other "fifth Beatles." The first was Andy White, who joined the group very briefly in 1962 because no one told George Martin that Ringo had been brought in to replace Best. So when Martin booked time for the group to record their first single ("Love Me Do"), Martin hired White - a session drummer - to supply the backbeat. Starr showed up to the studio to play, but Martin turned him away. According to Martin, Ringo was sore about the incident for years:

But not as sore as Ringo would be in the summer of 1964, when he developed a severe case of tonsillitis right before the group began a world tour. While he recuperated from surgery in the hospital, Jimmy Nicol - a session drummer from London - was asked to sit in behind the skins.

He also sat in for interviews:

3. Brian Epstein

A number of behind-the-scenes members of the group's business, production and management personnel have been credited as the "fifth Beatle." But aside from George Martin, the one that stands out most is Brian Epstein, who discovered The Beatles when they played at The Cavern in the early 1960s. He seized on the opportunity to become their manager and brought the group to fame. In 1967, he died of an accidental overdose of sleeping pills.

Here's The Beatles reacting to news of their manager's death:

4. Eric Clapton and Billy Preston

On September 6, 1968, Eric Clapton went to Abbey Road studios to work on "While My Guitar Gently Weeps." Harrison felt that Lennon and McCartney weren't taking his song seriously, so he asked the legendary guitarist to help him realize what he imagined for the bluesy ballad. Clapton allegedly told Harrison he didn't want to intrude because no other rock star had ever played on a Beatles record, but Harrison - revealing just how divided the band had become - said, "So what? It's my song."

Here's Harrison playing the tune with Clapton during The Concert for Bangladesh (1971):

Less than six months later, Harrison invited Billy Preston - a keyboarding phenom - to play organ on tracks including "Get Back," "Let It Be" and "Don't Let Me Down." His cheerful influence helped hold the group together as their unity continued to deteriorate.

Preston also joined the group for the rooftop gig in January 1969, their final public performance as a band:

5. George Martin

Clapton and Preston helped hold the group together during their slow disintegration, but Martin arguably made them a band worth keeping together. Martin not only served as producer but also mentor: "George Martin made us what we were in the studio," John Lennon said in 1971. "He helped us develop a language to talk to other musicians."

He also introduced the group to recording tricks that would hone their psychedelic style in the middle 60s. And he played piano on the bittersweet "In My Life" (1965). Check out the group's video for the song, which includes clips of the band along with many people credited as the fifth Beatle:

h/t Rolling Stone, Billboard, BBC, Beatles Bible, Guitar World