"He was a true gentleman and like a second father to me," McCartney wrote on his website Wednesday. "He guided the career of The Beatles with such skill and good humour that he became a true friend to me and my family. If anyone earned the title of the fifth Beatle it was George. From the day that he gave The Beatles our first recording contract, to the last time I saw him, he was the most generous, intelligent and musical person I've ever had the pleasure to know."
Revealing insight into the creative process that made Martin a key factor in The Beatles' success, McCartney added, "I brought the song 'Yesterday' to a recording session and the guys in the band suggested that I sang it solo and accompany myself on guitar."
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He continued: "After I had done this George Martin said to me, 'Paul I have an idea of putting a string quartet on the record.' I said, 'Oh no George, we are a rock and roll band and I don't think it's a good idea.' With the gentle bedside manner of a great producer he said to me, 'Let us try it and if it doesn't work we won't use it and we'll go with your solo version.'"
Martin's version of "Yesterday" has gone on to become one of the most covered songs in history, with Frank Sinatra, Elvis Presley, Ray Charles and Marvin Gaye being just some of the famous names to put their own spin on the hit.
"It was so thrilling to know his idea was so correct that I went round [sic] telling people about it for weeks," McCartney wrote, also noting that Martin had left "an indelible mark on my soul."
Then he signed off with typical wit, "God bless you George and all who sail in you!"
McCartney's fellow Beatle Ringo Starr reacted to the news on Twitter, writing, "God bless George Martin peace and love to Judy and his family love Ringo and Barbara George will be missed xxx."
God bless George Martin peace and love to Judy and his family love Ringo and Barbara George will be missed xxx— #RingoStarr (@ringostarrmusic) March 9, 2016
Minutes later, he tweeted a photo of Martin with the Fab Four, writing, "Thank you for all your love and kindness George peace and love xx."
Thank you for all your love and kindness George peace and love xxpic.twitter.com/um2hRFB7qF— #RingoStarr (@ringostarrmusic) March 9, 2016
Fellow record producer Quincy Jones was one of many music figures to echo McCartney's sentiment, tweeting, "RIP to my musical brother George Martin. We were friends since 1964, & I am so thankful 4 that gift. Bless u & your precious posse 4ever. Q"
RIP to my musical brother George Martin. We were friends since 1964, & I am so thankful 4 that gift. Bless u & your precious posse 4ever. Q-- Quincy Jones (@QuincyDJones) March 9, 2016
Mark Ronson took to Instagram, describing Martin as "the greatest British record producer ever." He added: "Thank you for everything."
Bryan Adams wrote simply, "Goodbye George Martin, thanks for producing the music that changed my world and everyone else's." The Canadian rocker's Instagram post featured a photograph he took of Martin at Buckingham Palace.
Writing on his personal blog, Queen guitarist Brian May added to the tributes, describing Martin's life as "a glorious innings!" and the man himself as "a gentle giant of popular music."
On Twitter, Lenny Kravitz added a posthumous reference to the recent death of fellow British music icon David Bowie, writing, "The legends are really going home! Visionary producer of #TheBeatles, George Martin (1926-2016)."
In a written statement, Abbey Road Studios – where Martin made magic with The Beatles – said Martin "transformed music recording with his creative flair, innovation and passion." The studio is "committed to ensuring Sir George's visionary legacy lives forever," the statement said.
A string of personal tributes have also flooded in from those who knew Martin personally, including Dhani Harrison, son of late Beatle guitarist George Harrison. He remembered the producer as a "dear sweet man" in an Instagram post.
Sean Lennon, son of the late John Lennon and Yoko Ono – who suffered from flu-like symptoms and was taken to the hospital last month – posted to Instagram. "R.I.P. George Martin," he wrote, including an early photo of Martin. "I'm so gutted I don't have many words. Thinking of Judy and Giles and family. Love Always, Sean."
RIP dad. I love you. I'm so proud to have been your son. I'll miss you more than words can say. Thank you for the all times we had together.-- Giles Martin (@mashupmartin) March 9, 2016
Fittingly, the most touching tribute was posted by Martin's son Giles Martin, who has followed in his father's esteemed footsteps to become a respected music producer in his own right.
"RIP dad. I love you," Giles posted to Twitter. "I'm so proud to have been your son. I'll miss you more than words can say. Thank you for the all times we had together."