Already fabulously rich, Thain will relish test as boss of Merrill

But Thain's greatest asset is not in his ability to strike headline-grabbing deals and multi-billion-dollar mega-mergers.

Instead, Thain is a master of the fine print, a technocrat who is as much about the nitty-gritty as he is about the bottom line.

When he joined the NYSE in 2003 his first deal was to join forces with Archipelago, a tiny electronic trading business that operated from America's west coast.

But the deal brought with it sweeping changes to NYSE's technology and opened the door for geographic and operational expansion.

Next came the stock market listing, giving the exchange instant currency to stitch up a big deal finally to transform NYSE into the global player it is today.

Merrill Lynch is used to the other kind of chief executive. The brash, pinstripes-and-braces Major-General who gets down among the troops to deliver regular rallying cries and isn't afraid of cranking up the risk. And some would argue that Merrill, with its 16,000-strong herd of thundering bulls, needs a big personality with a loud voice at the top.

But there is nothing wrong with Merrill's sales force. Where the bank has faltered is in its risk assessment of mortgage-backed securities and other debt-backed nasties. Indeed, Stan O'Neal, the former Merrill chief, was forced to go because he failed to keep track of some $8.4 billion worth of writedowns related to such debt-backed securities. Thain has hidden strengths in this area. It is often forgotten that the former NYSE chief was a bond trader from the mortgage-backed side of the fence. Indeed, he ran the mortgage desk at Goldman Sachs from 1985 to 1990, whereupon he was appointed president of the investment bank, a fitting gold star for his successes.

Thain accumulated much of his vast personal wealth at Goldman. As one of the senior players at the time of the bank's flotation in 1999, he collected around $150 million.

The size of his private home in Rye, a country village in New York's Westchester County, is testament to that. It is so big, in fact, that he pays property taxes in excess of $150,000 a year in two different towns 34 - Harrison and the City of Rye. The property is so big that it also sneaks across the boundary of Rye Brook, another village.

The $10 million mansion, in at least 10 acres of grounds, includes a small farm and several beehives, from which Thain used to collect honey with his youngest son each morning. It has 14 bedrooms and two swimming pools. A river runs through his back garden, feeding a lake stocked with fish.

But Thain's country home's worth is small compared with the $27.5 million he has just spent on a two-storey luxury apartment on Park Avenue in Manhattan.

He and his wife often host lavish parties, most recently holding a fundraiser for John McCain, the Republican Presidential hopeful.

Merrill has bought itself one of Wall Street's biggest rainmakers. His new job is his hardest yet. Unlike at Goldman, where he made his name striking deals as a solo operator, and at the NYSE, where he inherited an institutional monopoly, at Merrill he is going into a bank where morale has been shattered.

He will have to move incredibly quickly to prevent Merrill's key earners from leaving and to restore confidence.

After Goldman and NYSE, the coming months will show if he can complete a remarkable hat-trick.