The sign behind Jack Grubman's desk used to say it all. In large block capitals, it declared the mantra that helped to make the telecommunications stock analyst a Master of the Universe during Wall Street's biggest bull market: "BUY NOW".

But those days are gone, and the man who, more than any other, fuelled the telecoms bubble of the late-1990s has become a decided liability for Citigroup, his employer until this week.

Many of the companies he once avidly promoted are bust. Swashbuckling executives he helped to turn into superstars - among them Mr Bernie Ebbers of WorldCom and Mr Joseph Nacchio of Qwest - are gone, under investigation for their role in the massive destruction of shareholder wealth that has followed the bubble years.

With regulators and politicians looking for culprits to blame for the debacle in the US financial markets, Mr Grubman has himself become a prime target, to many a symbol of what was wrong about the way Wall Street worked during the boom years.

For Sandy Weill, chairman of Citigroup, the 48-year-old analyst has finally become too hot to handle. This week Salomon Smith Barney, Mr Weill's investment banking arm, acted to cut its ties with Mr Grubman, requesting his resignation - though at a price. The man who once pulled down some eye-wateringly large pay awards, even by the standards of Wall Street, will walk away with $32 million (€31 million). Salomon will meet his legal bills - no small matter, given the blizzard of arbitration claims he faces from investors.

His departure is a seminal moment in the unravelling of the bull market. To critics, he embodied the untenable conflicts of interest that characterised the boom years. He tried to bridge the traditional gulf between investment banking and equity analysis - between being a confidential adviser to corporate chieftains and an independent commentator on their companies.

Like Michael Milken, the junk bond impresario who came to symbolise the excesses of a previous era, Mr Grubman became an important cog in the machinery of the financial world, attracting both sophisticated institutional investors and powerful executives in a way that appeared to benefit both sides.

But while Mr Milken eventually served prison time after pleading guilty to securities fraud, the investigations into Mr Grubman have yet to turn up evidence that would support a criminal case.

It was sheer force of will that put Mr Grubman at the very centre of the 1990s bull market.

The only son of a blue-collar family in Philadelphia, he did not have the sort of privileged background that has long made Wall Street a haven for the wealthy elite. Taking after a father who spent several years as a professional boxer before a job in the local highways department, Mr Grubman himself became a fighter and an avid follower of boxing.

The pride in his boxing background - evident from the boxing posters and gloves on display in his office at Salomon - also points to a pugnacious character and a doggedness that enabled him to claw his way to prominence. After a degree at Boston University and post-graduate work at Columbia, the young mathematics whizz alighted at AT&T in the late 1970s. The eight years he spent there before becoming an analyst at PaineWebber set him apart on Wall Street, giving him the sort of direct industry experience that few investment analysts gain.

It was a single, powerful idea that finally set him apart from the herd. The telecoms industry was on the brink of a revolution, he predicted.

With fibre-optics transforming the economics of the business, it was possible to build new global communications networks from scratch and undercut long-established companies that were tied to old technologies.

With Mr Grubman providing much of the intellectual framework, Salomon - where he had moved in the early 1990s - played a key role in raising the cash and masterminding the mergers that brought this vision to life. Mr Grubman had little time for old-time companies like AT&T: newcomers like WorldCom, Qwest and Global Crossing were the future. His uncompromising views coincided with an unprecedented investment boom.

Mr Grubman's success made him hot property on Wall Street. Goldman Sachs tried to lure him away from Salomon in 1998 - an attempt that only added to his mystique and his already considerable pay packet. By the late 1990s he was widely rumoured to be making more than $20 million a year. Part of his $32 million payoff this week stems from the forgiveness of a loan that was extended to him to keep him at Salomon in 1998. He now lives in a townhouse on Manhattan's Upper East Side, which was recently equipped with powerful electronics to allow him to use the firm's secure computer system from home.

The rags-to-Wall-Street-riches story may be genuine, but Mr Grubman was not above a bit of self-mythologising along the way. He once maintained, wrongly, that he came from the poor South Philadelphia area made famous by another, fictional boxer - Rocky Balboa. And he confessed to sprucing up his resume with a claim that he attended the Massachusetts Institute of Technology.

Inside Salomon, his aggressive and uncompromising approach also made him a controversial figure - as did his close involvement in the firm's deal-making. According to some former colleagues, Mr Grubman was a bully who often acted as though he ran the firm's telecoms group. His reach went beyond research and affected the investment bankers who worked with the companies, too. "Jack would be the first to say he wanted to be an investment banker," says one former Salomon banker.

His protectiveness towards the companies he recommended went so far that he practically chose which investment bankers would work on which accounts, according to one associate. If he deemed a banker unworthy of working for one of his clients, he would sometimes tell the client not to co-operate. "Having him behind you meant whether you would produce revenues or not," says a former Salomon banker.

That sort of power created headaches for Salomon's legal and compliance officers, who were usually a few steps behind him. The firm often had at least two compliance officers following up on Mr Grubman's reports, concerned that his high profile and the possible conflicts between his work as analyst and adviser would rebound.

Mr Grubman was unapologetic about his style of operation when he appeared before a sceptical congressional committee in June. His defence of his position, made at the height of the bull market, was disarmingly simple. "What used to be a conflict is now a synergy," he told Business Week. He argued that he could benefit both companies and advisers by being close to both. It remains to be seen whether that will convince Eliot Spitzer, the New York attorney general, who has been examining Mr Grubman's role.

Yet few of those who know Mr Grubman accuse him of the kind of bad faith apparently displayed by another analyst investigated by Mr Spitzer - Henry Blodget of Merrill Lynch. While Mr Blodget recommended some stocks publicly while criticising the companies in private, Mr Grubman's belief in his industry never wavered. "He had a conviction and he sold that conviction," says one former colleague.

That conviction was on display almost to the end. Mr Grubman was still recommending WorldCom - the company with whose rise he is most closely associated - until this spring, only finally turning negative on the stock four days before it disclosed a $3.9 billion fraud. Having helped to mastermind the company's rise - and to generate hundreds of millions of dollars of fees for Salomon - he was faithful to the end.