For almost 40 years, Maurice Gibb was the ever-smiling backbone of a band that pushed back the limits of chart success and musical diversity. From plaintive laments with complex lyrics to upbeat disco crooning, the Bee Gees achieved worldwide sales of more than 100 million albums. They are the only artists to have scored number one hits in each decade from the 1960s to the 1990s, at one point scoring six consecutive number ones in a row. Saturday Night Fever, to which they contributed five tracks, remains the bestselling soundtrack album of all time, and Stayin' Alive, If I Can't Have You, Night Fever, Tragedy and How Deep is Your Love? were all enormous hits.

The group’s falsetto harmonising epitomised the peculiar fragile glamour of 1970s’ pop, and even at the time was often parodied. As soon as punk came along, the Bee Gees sounded and looked as outdated as perukes or knee-breeches. They did manage later revivals, despite a long history of personal problems, but in 1997 they stormed out of a mocking television interview by Clive Anderson. Popular though it was, their music never sounded grown-up, and Anderson had failed to realise that, unlike everyone else, they took it entirely seriously.

Maurice and Robin Gibb were born in 1949 in Douglas, Isle of Man. Although they were twins, their different personalities became clear early on: while Robin was an intense thinker, Maurice was always affable and friendly, the most open and straightforward of the elder three Gibb brothers. Despite extraordinary success, Maurice would never lose his natural humility, always maintaining that there was nothing very special or different about him. The most approachable and musically versatile, Maurice made most effort not to become hidden behind bodyguards and assistants, and suffered most visibly as a result of the band’s rows, break-ups and tragedies — most cripplingly the death of the trio’s youngest member, Andy, in 1988.

Their mother, Barbara, was a singer, and their father, Hughie Gibb, led a big band in Manchester when the family moved to Chorlton-cum-Hardy in 1955. The brothers were encouraged to develop their talents, Maurice later recalling that, when the twins sang to elder brother Barry’s guitar at the age of six, their father was convinced he was listening to the radio. Robin and Maurice first learnt music on plastic banjos, and soon afterwards the trio played as a child act called the Rattlesnakes, or sometimes Wee Johnny Hays and the Blue Cats, around Manchester’s cinemas.

In 1958 the family emigrated to Australia. While Robin and Barry were refining their vocal style, Maurice concentrated on music, becoming skilled on guitar, bass and keyboards, and later proficient on the drums. By 1963 the brothers had attracted the attention of an Australian record label and signed up as the Bee Gees. Their first big hit in Australia came in 1966 with Spicks and Specks.

While the record climbed the Australian charts, the brothers flew to London to audition for Robert Stigwood, a director of NEMS Enterprises, the company owned by Beatles mastermind Brian Epstein. Polydor signed them and released their intriguing British debut single, New York Mining Disaster, 1941. Early reviews compared the brothers to Maurice’s idols, the Beatles. He never forgot meeting them for the first time, or the astonishing excitement of going in a few short months from reading about them in teen magazines to living next door to Ringo Starr. With a shudder, he would also recall being handed his first drink — a scotch and coke — by John Lennon at the age of 16.

A year later the group reached number one in the charts with Massachusetts. Maurice quickly fell into the pop star life, spending more and more time in West End nightclubs and spending huge sums of money. Strains had already begun to be felt within the group, as Maurice and his twin rebelled against the “democratic dictatorship” of the more showbusiness-savvy Barry.

In 1969 Maurice married the singing star Lulu, but the union was not a happy one. Maurice’s six Rolls-Royces and eight Aston Martins were the most visible sign of how jaded he had become with wealth, battling against boredom with increasingly lavish spending and longer drinking binges. Lulu later said that their house was “positively polluted” with Maurice’s clothes, jewellery and gadgets.

When the marriage ended four years later, journalists assumed that softlyspoken Maurice had been cowed into submission by the strident singer. But he acknowledged that just before the split he had crossed an “invisible line” with his drinking, after which it took complete hold of him. He struggled with this problem, while refusing to acknowledge its hold, for more than 20 years.

Creatively, however, he was at his zenith. In 1975 the brothers decided to work with the producer Arif Mardin, who was well-known for his work with soul acts such as Aretha Franklin. Mardin taught the brothers how to work a dance beat into their music. Maurice also developed his distinctive bass style at this time, and it was prominent on the album Main Course.

“There’s a bridge that we had to cross on the way to the studio,” Maurice remembered. “And every time we crossed it, the car would make a clickety-clack sound. After a few days of this, we realised that the clickety-clack rhythm was perfect for a song.” Maurice turned the song into Jive Talkin’, taking the funk-based path that the Bee Gees would continue to follow.

Worried that the band’s careers had reached an impasse, Stigwood arranged for them to compose the music for a film meant to catch the spirit of the disco era, Saturday Night Fever (1977). Starring John Travolta, the film portrayed the lives of Italian immigrants in Brooklyn living for the excitement of Saturday’s disco dancing. The Sunday Times called it “an urban safari into darkest America”, and it was hugely successful, but for all the riches it brought the Bee Gees Maurice complained that the film was “tacky and shoddy” and blamed it for ultimately destroying the band. The following year saw them in a lacklustre cinema tribute to the Beatles, Sgt Pepper’s Lonely Hearts Club Band.

Then suddenly, despite their huge success with Spirits Having Flown in 1979, the public turned away from disco music, and the brothers found themselves trapped by the “medallion man” image of Saturday Night Fever. Their 1981 album Living Eyes failed to sell, and the band split. Stigwood accused the brothers of fraud, libel and blackmail in a multimillion-dollar lawsuit, and all three brothers increased their intake of chemicals as they struggled to survive their straitened fortunes. For a time only their lawyers communicated.

During that decade, however, the brothers worked with Barbra Streisand on her Grammy-winning hit Guilty, and with Diana Ross, Dolly Parton and Kenny Rogers.

In 1987 the Bee Gees reformed with the album ESP and its hit track You Win Again. For Maurice, now sporting the goatee, black clothes and fedora that became characteristic, the reunion was a great relief and one he had longed for. The respite was shortlived, however, for Andy, whose success in the mid-Eighties had served to underline the Bee Gees’ fall from grace, died from excesses of cocaine and alcohol. “After that, I just drank to numb my mind,” Maurice said.

With the support of his children and wife Yvonne, Maurice finally faced his problems and emerged from a rehabilitation clinic in 1991. On a BBC programme, Fighting Back, he admitted that he realised the extent of his addiction after pointing a gun at his family.

He relapsed briefly in 1994, but remained happy, sober and creative from then until his death. In 2001 the Bee Gees released This is Where I Came In, a mature, cheerfully cynical album that reflected the brothers’ trials and sense of having seen it all before, along with a greatest hits collection.

The Bee Gees were each appointed CBE in 2002. Maurice lived, like his brothers, in Miami Beach, Florida. He is survived by his wife and by a son and a daughter.

Maurice Gibb, CBE, musician and singer, was born in Douglas, Isle of Man, on December 22, 1949. He died in Miami following a heart attack during abdominal surgery on January 12, 2003, aged 53.