Sir Paul McCartney and Ringo Starr have led tributes to Sir George Martin, the record producer known as the Fifth Beatle, who has died aged 90.
His family confirmed he died peacefully at his home on Tuesday and thanked "everyone for their thoughts, prayers and messages of support".
Sir George helped The Beatles achieve global success, producing their early 1960s pop recordings to their classic albums Revolver and Sgt Pepper's Lonely Hearts Club Band.
Sir Paul described him as a "true gentleman and like a second father to me", while Starr praised the producer's "love and kindness" to the Fab Four through the years.
"If anyone earned the title of the Fifth Beatle it was George," Sir Paul said.
"The world has lost a truly great man who left an indelible mark on my soul and the history of British music. God bless you George and all who sail in you!"
Sir Paul also recalled his favourite memory of Sir George when he persuaded the former Beatles star to include a string quartet on the band's classic hit Yesterday.
"His idea obviously worked because the song subsequently became one of the most recorded songs ever with versions by Frank Sinatra, Elvis Presley, Ray Charles, Marvin Gaye and thousands more," he added.
Ringo Starr broke the news of Sir George's death on Twitter as he wished "peace and love" to his family.
He posted a picture of The Beatles and Sir George with the caption: "Thank you for all your love and kindness George peace and love."
Sir George's son Giles, who is also a producer and has worked at Abbey Road studios, tweeted: "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."
Meanwhile, Sir George's manager Adam Sharp said: "The family would like to thank everyone for their thoughts, prayers and messages of support.
"In a career that spanned seven decades, he was an inspiration to many and is recognised globally as one of music's most creative talents. He was a true gentleman to the end."
Sir George, a carpenter's son from Holloway in north London, studied at Guildhall School of Music and played the oboe professionally before joining the recording industry.
During his early career, Sir George produced comedy and novelty records in the early 1950s, working with Peter Sellers and Spike Milligan.
He was head of the Parlophone record label when he first heard The Beatles's demo tape in 1962, with the band releasing their first single Love Me Do in October of that year.
Their third single From Me To You went to number one in April 1963 - the first of 17 chart-topping hits.
As well as producing records for The Beatles, he worked with a host of artists including Gerry and the Pacemakers, Sting and Celine Dion. He also produced two James Bond themes - Shirley Bassey's Goldfinger and Live And Let Die by Paul McCartney and Wings.
During his career, which spanned seven decades, Sir George won two Ivor Novello awards, six Grammys and in 2008 was the recipient of the Grammy Foundation's Leadership Award which saluted his humanitarian work.
In 1965, he was nominated for an Academy Award for his work on the music in A Hard Day's Night and in 1984 he received the Brit award for outstanding contribution to music, having been named best British producer at the first Brit awards in 1977.
Sir George, who is survived by his wife Judy Lockhart-Smith and four children, received his knighthood in 1996. A year later he produced Elton John's re-write of Candle In The Wind for the funeral of Diana, Princess of Wales - which went on to become the biggest-selling single of all time.
In 2002, Sir George was part of the team which organised the Queen's Golden Jubilee concert at Buckingham Palace, an event headlined by Sir Paul.
A statement from George Harrison's widow Olivia and son Dhani read: "George Martin was a gentleman above all. May he rest in peace. Our thoughts are with Judy & the family at this sad time."
Sean Ono Lennon, the son of John Lennon and Yoko Ono, posted a picture of Sir George on Instagram with the caption: "R.I.P. George Martin. I'm so gutted I don't have many words."
Prime Minister David Cameron tweeted: "Sir George Martin was a giant of music - working with the Fab Four to create the world's most enduring pop music."