Standing in a cable car as it gently ascended a Swiss mountainside, he cut an unremarkable figure. His fellow passengers knew he was an accomplished skier: they had seen evidence of that over the previous few days as he whistled down the slopes in the resort of Verbier. But, with his shaggy hair and scruffy clothing, he was not a man who worried too much about his appearance. He didn’t stand out.

Yet as he surveyed the snowscape below, this quietly spoken 36-year-old Australian was contemplating one of the most spectacular career moves ever made by a hedge-fund manager. Greg Coffey was weighing up a choice — should he remain in his very well-rewarded position as a star manager controlling $7 billion (£3.5 billion) of funds for GLG, one of the world’s largest hedge-fund groups; or should he go it alone and set up his own operation?

He knew that leaving GLG would mean a huge sacrifice — he would be giving up $250m in GLG shares that he could have cashed in had he stayed at the firm for a further five years.

It was an enormous decision to make, and he talked it through with his wife, Ania Brzezinski, a former financial analyst with Credit Suisse First Boston. They also discussed the idea over dinner with friends. One recalls having such a conversation with Coffey as they were being hauled up the mountain in a cable car. “It’s funny because although Greg is a great skier he dresses like a bum on the slopes,” he said. “He wears these shabby, old ski pants and a little bobble hat. And here he was, talking about going it alone.”

Few people in the cable car would have suspected the man in the bobble hat was one of the most successful hedge-fund managers of his generation. And they certainly wouldn’t have realised that he was pondering a decision that would reverberate throughout the global hedge-fund industry.

By the time he returned to London earlier this month, Coffey’s mind was made up. He had earned a fortune with GLG — a reported $300m last year alone. Within days of finishing his holiday, however, he had told GLG that he wanted to leave to set up his own hedge-fund operation.

The company’s directors were shocked. They pleaded with him to hold back his resignation while they thought up ways of persuading him to stay. Coffey agreed to the delay, but the lure of being his own boss was too great. Last week, a stock-exchange announcement said he would be leaving GLG in six months.

For GLG, losing Coffey is a huge blow. He has been with the firm for five years. His early career was unremarkable: he graduated with a degree in actuarial studies at Australia’s Macquarie University and started work at Macquarie Bank in 1993. He went on to work for a fund backed by George Soros, then, when that ran into trouble, he was introduced to GLG.

He wasn’t offered work with GLG straightaway, but he kept in touch, and eventually Philippe Jabre, then a partner in the firm, offered him a job.

The position was menial — Coffey was carrying out trades on behalf of more senior dealers — but Jabre recognised his talent, and within a year Coffey was managing the emerging-markets segment of a larger fund.

A former colleague recalls Coffey being very insecure at the beginning. “He even made a number of mistakes that could have cost him the job,” said the former workmate. Coffey survived, though, and in late October 2005 took charge of his own fund.

The timing was perfect. Emerging-market equities did well, and Coffey’s fund performed brilliantly. Within a short time, investors were scrambling to put millions into his hands. The team round him grew from 6 to 13 people, and it was soon clear that Coffey was in effect running a firm within a firm.