Allen Klein was the self-styled "biggest bastard in the valley" who managed the business affairs of both the Beatles and the Rolling Stones for a brief period in the late 1960s.
But the tough-talking New Jersey accountant, who died on Saturday night aged 77, was to fall out in spectacular fashion with his two most high-profile clients, igniting years of litigation and courtroom battles.
His death at his New York home following complications from Alzheimer's disease was announced by his company, ABKCO Music & Records, which still owns the rights to a major swath of the Stones' most successful 1960s recordings. Despite the deep-seated acrimony his involvement with both bands engendered among musicians and fans alike, his publicist Bob Merlis said the archetypal music mogul continued to believe he had done a good job for the acts he represented. "[He was] very proud of the position he was in and what he was able to do with the different artists he was able to work with," Mr Merlis said.
Many Beatles fans blamed Klein, a brash, short-tempered man, for adding to the pressures which eventually fractured the Fab Four, although the truth is that the band had most likely run its course by the time he assumed partial control of their affairs in 1969. Klein found himself drawn into the increasingly hostile rivalries between John Lennon and Paul McCartney.
A first attempt to sign them at the height of their fame after the death of Brian Epstein in 1967 had failed. But Klein, whose interest in music many suspected extended little beyond the financial bottom line of the acts he courted, persevered. He managed to persuade Lennon, who in turn convinced George Harrison and Ringo Starr to take him on board, partly because of his fearsome reputation for chasing unpaid royalties (half of which he kept as reward) for the likes of Bobby Darin and Sam Cooke while talking tough to record companies, but also because he provided a viable alternative to McCartney's chosen successor, his father-in-law, the New York attorney Lee Eastman.
But Lennon insisted there was a deeper link between the men who met on the set of the Stones' film, Rock and Roll Circus. In a 1970 interview, he said: "He not only knew my work, and the lyrics that I had written, but he also understood them, and from way back. That was it."
Lennon was later to reconsider his view, largely because he believed Klein had slighted Yoko Ono. His 1974 track "Steel and Glass", which carries the lyrics "Your mouthpiece squawks as he spreads your lies", is believed to be a reference to the former manager. Klein was later ruthlessly parodied as Ron Decline played by Jon Belushi in the 1978 film The Rutles.
But although Klein was never accepted by McCartney, he helped sort out the chaos of the cash-strapped band's doomed Apple ventures, albeit with a ruthlessness at odds with the prevailing hippy ideology of the time. He also helped renegotiate a lucrative deal with EMI and is credited with helping save the Let It Be project by bringing in the US producer, Phil Spector. In a 2001 interview, he admitted that his prime interest was money, not music. "It was going over the books that I loved," he said. "And I was good at it."
In 1969, a New York Times profile referred to him as "the toughest wheeler-dealer in the pop jungle". It was a view he readily shared, having sent out a Christmas card parodying the 23rd Psalm, which read: "Yea though I walk through the valley of the shadow of death, I will fear no evil, because I'm the biggest bastard in the valley."
He had co-managed the Stones since 1965, having bought out Andrew Loog Oldham's share in the band, and was reaping a 20 per cent management fee after renegotiating a record deal on their behalf. But by the fag end of the decade the relationship between Klein and particularly Mick Jagger was disintegrating. The sticking point was his acquisition of the rights to the Stones' best work including classics such as "Brown Sugar", "(I Can't Get No) Satisfaction" and "Jumpin' Jack Flash".
He was eventually fired in 1970, the year of the Beatles official split when McCartney sued his former band mates largely in an effort to rid himself of Klein. But he continued to exert considerable control over the fortunes of both the Beatles and the Stones for years, enmeshing them in a tangle of complex legal disputes that bamboozled fans. Tensions with the business-minded Jagger persisted even after Klein was sacked, culminating in a famous incident in which the singer chased a retreating Klein down the corridor of the Savoy hotel after a bad tempered discussion over money. With the American in control of much of their back catalogue, the Stones had failed to reap the financial rewards they felt entitled to. The acrimony was only settled – legally at least – in 1984 when Jagger gave evidence before a federal court in New York in which he complained that Klein "wanted a hold on us, on our futures".
Fellow songwriter Keith Richards took a less confrontational view of the relationship with Klein, describing it as "the price of an education". Klein eventually kept the rights to the songs but agreed to pay royalties promptly. By this time in 1979, he had already served two months in prison for tax fraud, failing to report income from sales of promotional records.
But he insisted he had merely been doing his job. "Don't talk to me about ethics," he had told Playboy in 1971, the year he helped produce George Harrison's Concert for Bangladesh, the forerunner of Live Aid, although it eventually took a decade for proceeds to reach their intended recipients, a result of disputed tax arrangements. "Every man makes his own [ethics]. It's like a war. You choose your side early and from then on you're being shot at. The man you beat is likely to call you unethical. So what?"
Klein's company ABKCO Music & Records is among the biggest independent labels in an industry dominated by a handful of megalith multinational corporations. It is to remain family-controlled, with two of the children continuing to work there, including the head, Jody Klein.
In 1997, the Klein family showed their ferocious business instincts remained undimmed: the British band The Verve were forced to hand over 100 per cent of their royalties from their biggest hit, "Bittersweet Symphony", because it had used too much of a sample from the Stones' hit "Last Time", the rights to which were retained by ABKCO.
Meet the management: Rock's A-list
* Malcolm McLaren The former shop-owner masterminded the short but explosive career of the Sex Pistols by exploiting the anger of 1970s disaffected youth. Fell out with the lead singer Johnny Rotten then embarked on his own successful solo career.
* "Colonel" Tom Parker A Dutch immigrant, he bought out a young Elvis Presley from his record contract and ruthlessly built both their careers. He earned a huge slice of the King's earnings, his cut eventually exceeding Presley's. He died in Las Vegas in 1997 aged 87.
* Peter Grant Took control of Led Zeppelin after The Yardbirds split. Grant, a huge former bouncer and wrestler, safeguarded the band's financial and artistic affairs with forthright determination. Died in 1983 aged 60.
* Don Arden The father of Sharon Osbourne guided Black Sabbath, the Electric Light Orchestra and the Small Faces. An obituary said his methods included "beatings and deployment of muscular assistants, sometimes with firearms". Died in 2007 aged 81.