If sheer brainpower is what Wall Street needs to find its way out of the wreckage of the credit squeeze then things are looking up.

This week, Citigroup named as chief executive Vikram Pandit, a cerebral strategist with a degree in electrical engineering and one of the best minds in the business. Last month, Merrill Lynch named as chief executive John Thain, another cerebral strategist with a degree in electrical engineering and one of the best minds in the business.

But there is more to running a company, particularly one as large, diverse and troubled as Citigroup, than intellectual brilliance. Unlike Mr Thain, Mr Pandit has no experience of running a public company and some observers question whether he has the right skills to take on such a challenge. Indeed, many think it is too big for anyone and predict that before long Mr Pandit will be forced to break up the company.

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For those who were hoping for a high-profile heavy hitter with a big personality to replace Chuck Prince - the former lawyer who quit last month as chairman and chief executive after four embattled years in the job - the news came as a disappointment.

Around a conference room table, Mr Pandit, 50, is affable, charming and impressive. But even his best friends do not claim he is a great crowd pleaser. He has kept out of the limelight for most of his career and received poor reviews for his defensive performance on his first conference call with analysts this week.

"We needed someone like Sandy Weill to get the place excited again, and he ain't it," said one shareholder, referring to Mr Prince's predecessor who built Citi through a series of deals in the 1990s. 

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But Mr Weill himself, who has known Mr Pandit for 15 years, says he is "thrilled" with the appointment. With hundreds of millions of dollars in Citi shares, even after this year's slump in the stock price, Mr Weill has more at stake than most. "He is the right guy to get the people to pull together and get Citi back on track to be the global leader in financial services," says Mr Weill, who is not concerned about Mr Pandit's lack of experience of retail financial services which provide more than half of group profits.

Another person who is convinced Mr Pandit is up to the job is his father Shankar, an 84-year-old former pharmaceutical executive, who told The Times this week that his son had lived up to his expectations. "He was a brilliant boy. In school, he always stood first in his class."

Born in Nagpur, Mr Pandit left India when he was 16 to go to New York's Columbia University. After his first degree he did a PhD in finance and worked as a professor at Indiana University before joining Morgan Stanley .

Rajnish Mehra, who was on his thesis committee at Columbia, said he was assigned one of the toughest topics they could find: recursive competitive equilibrium in the case of heterogeneous households. "We had no idea how to solve it so we gave it to him and he made good progress."

Mr Mehra recalls that Mr Pandit was not only "incredibly bright" but also very happy. "He really seemed to be at ease with himself." Friends say he remains so -- "he is saner than almost anyone I know on Wall Street", says one - partly because of his happy family life. He and his Indian-born wife, Swati, have two teenage children.

"He is a very simple person at heart," says his father. "He derives pleasures from simple things in life, not playing golf etc.." He was mortified, friends say, when the New York tabloids recently reported that he had paid $17.8m for an apartment on Central Park West previously owned by actor Tony Randall.

When Mr Pandit walked out of his job at Morgan Stanley in 2005, few people would have predicted that little more than two years later he would be running one of the biggest companies in the world. He quit following a reshuffle in which he was passed over for the number two job to Phil Purcell, the then chairman and chief executive. The move ignited a battle over Mr Purcell's leadership which led to his resignation three months later.

There are sharply divided opinions about Mr Pandit among those who worked with him during his 22 years at Morgan Stanley. He had a highly successful career, particularly running Morgan Stanley's equities business, but in his final years as head of its institutional securities operations some fellow executives complained that he was a poor decision-maker and was risk averse.

The latter charge rings rather hollow these days as banks such as Citi and Merrill nurse billions of dollars in losses from ill-judged risk-taking on mortgage-backed securities.

Admirers also deny the criticism of his decision-making. Glenn Hubbard, former chairman of President George W. Bush's Council of who is now Dean of Columbia Business School, says he is "one of the smartest people I have ever met" in business and academia. "He has a professorial manner but he is not professorial to the point of not making decisions." He adds that Mr Pandit, who sits on the Columbia board, is "collaborative and collegial".

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Many former Morgan Stanley executives have a very high opinion of Mr Pandit, including Mr Purcell, who believes he is "up to the challenge" of Citi. Another former executive says: "He is a great strategist but he is also a nuts and bolts guy who really gets things done."

A number of senior Morgan Stanley colleagues had enough confidence in him to follow him out of the door to set up a hedge fund. Earlier this year, Mr Prince paid a reported $800m for the fund, which was not very successful, largely to get his hands on Mr Pandit, whom he swiftly promoted to head all Citi's institutional businesses.

One of his biggest fans is Robert Rubin, the former US Treasury secretary who has been on the Citi board for eight years, and was a prime mover behind his appointment. Despite Citi's huge mortgage problems, a weakened balance sheet and a loss of talent in recent years, Mr Rubin insists it still has "the best hand to play in financial services".

Mr Pandit has given little indication of how he will play that hand. He has promised a review of all Citi's businesses, which some investors hope might lead to big disposals, even a break-up. But the betting is that he will keep it together.

Mr Weill admits the group he built does not make sense if it is not managed right. "But if it is managed right it makes all the sense in the world. And Vikram has the ability to do it."

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