In March 2005, shortly after realising he had lost out on the second most powerful job at Morgan Stanley, Vikram Pandit put on his coat and walked into the New York evening, never to return to the bank he had joined more than two decades earlier.

Former colleagues recall he slipped out almost unnoticed, without tearful farewells or parting shots to colleagues. That low-key demeanour has characterised Mr Pandit ever since he left his native Nagpur, in central India, and moved to New York to attend Columbia University in the early 1970s.

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But as chief executive of Citigroup - the ailing financial behemoth he has been running since December - Mr Pandit's efforts to stay out of the limelight have been fruitless. Citi's share price has disintegrated amid fears it will add billions of dollars in fresh losses to the $50bn-plus (pound 34bn, euro 40bn) in writedowns it has already suffered. This week the shares halved, putting the 51-year-old executive under huge pressure to save Citi, and himself, from a grim future, which could involve a fire-sale, a break-up, or even a government takeover.

Mr Pandit's allies within Citi - a company that has often been riven by infighting among rival factions - insist that he can lead the bank out of the turmoil. "Do I think he is the right guy to pull Citi out of this? Yes," says Stephen Volk, one of Citi's many eminence grises who has known Mr Pandit for decades.

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Mr Pandit professes not to be concerned by the prospect of going down in history as Citi's last chief executive. "I have a lot of worries. That is not one of them," he says.

But Citi's stunning decline has increased the scrutiny of Mr Pandit's personality and management philosophy and raised questions over whether his methodical, technocratic style is what the company needs to survive. When asked to point out Mr Pandit's most visible attributes, friends and foes point to his sharp mind and calm, professorial manner.

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Mr Pandit started out in academia, teaching economics at Columbia - where he obtained all his four degrees - and then finance at Indiana University, finishing what now seems a prescient doctoral dissertation, "Asset Prices in a Heterogeneous Consumer Economy".

After being hired by Morgan Stanley as a consultant, Mr Pandit, who had already abandoned his first intellectual love, engineering, caught the Wall Street bug. In 1983, he joined the bank where his skills as an expert trader and prudent risk manager propelled him to the top of its investment banking division. He quickly earned a reputation as a driven banker who was often the smartest person in the room and knew it, too.

"Everybody at Morgan Stanley knew that, in a meeting with Vikram, you were dead if you checked your brain at the door," a senior banker recalls.

Despite being a Wall Street star, Mr Pandit steered clear of the glitzy trappings - golf, flashy cars, wines and cigars � craved by most bankers. He devotes most of his free time to Swati, his wife of over 20 years, and their two children. Indeed, news that he had spent $17.8m on a Central Park West apartment previously owned by the late actor Tony Randall made the tabloids partly because it contrasted with his relatively frugal lifestyle.

After his bitter departure from Morgan Stanley, Mr Pandit struck out on his own, founding Old Lane, a hedge fund that was sold to Citi for a hefty $800m last year. At the time, Citi executives hinted that the real reason for the deal, which yielded Mr Pandit a $165m payout, was the purchase of his talents.

Old Lane had an inglorious end. It was closed down by Citi earlier this year after poor results. Mr Pandit, however, has thrived. Initially put in charge of Citi's hedge funds business, he was quickly promoted to head the securities division until the bitter ousting of Chuck Prince gave him the chance to claim the CEO title he had coveted at Morgan Stanley. His elevation was backed by Citi's influential power-brokers, such as Robert Rubin, the former US Treasury secretary, and Sandy Weill, the former CEO, who publicly anointed him as the bank's saviour.

To his critics, however, Mr Pandit's sharp mind and passion for intense analysis - often carried out alone with only spreadsheets for company - have hindered his development as a chief executive. "He is not a leader of people, he is a quantitative trader who overanalyses things and can take ages to make tough decisions," says a former Morgan Stanley banker.

Some current colleagues agree, saying that the charm and clarity of thought he displays in small gatherings often disappear in front of large audiences of employees or clients. Mr Pandit has worked hard to dispel that impression. Earlier this year, he gave a passionate, often tempestuous, performance at a staff meeting after Citi had been beaten in the race to buy the regional lender Wachovia.

But he admits that the turbulent events of the past few months have made him reconsider his approach.

"Analytics works when markets work analytically but in these markets you need to make decisions fast and I find myself turning to my instincts more and more," he says.

He has told friends that he is frustrated, and often angered, by the destruction of shareholder value that is taking place under his watch but remains determined to carry out his task: cleaning up Citi's balance sheet and reviving its fortunes.

So far, Citi's strategic needs have played to his strengths. The bank needed capital and he raised $50bn from investors earlier, and on better terms, than many rivals. Expenses and toxic assets had to be reduced and he set about the job with the zeal of a proven risk manager.

But Citi's woes might call for more visionary and charismatic leadership than he can offer. Sir Win Bischoff, Citi chairman, who has also come under internal fire, says those fears are unfounded. "In the current environment, I would rather have a leader who is very good at understanding the nuts and bolts of the business than a glad-handing type."

Mr Pandit points to his traditional Indian upbringing as a source of calm. "I cannot deny that a piece of my Indian upbringing stayed with me," he says. "As I go about my life, there is a clear sense of Karma, that the tide is going to come and go and the main thing you have to do is influence where you are on the tide."

Citi's shareholders must hope he will not be swept away by the waves of selling that have rocked a once-dominant financial group.