Merrill Lynch & Co Inc on Wednesday named NYSE Euronext Chief Executive John Thain as its new CEO, a move that acknowledges it needed an outsider with a Goldman Sachs pedigree to repair an image battered by wrong-way bets on subprime mortgages.

Thain, 52, replaces Stan O'Neal, who was ousted as Merrill's CEO and chairman last month after the company wrote down $8.4 billion in assets during the third quarter.

Thain's appointment is effective December 1, Merrill said. One of his first tasks will be to assess Merrill's risk management procedures, which analysts said clearly failed in evaluating exposure to subprime mortgages and collateralized debt obligations.

John will be adept at balancing the focus on risk management and controls while taking the steps necessary the company evolves and grows, Merrill nonexecutive chairman Alberto Cribiore said in a statement.

Merrill shares are down 38 percent this year, erasing about $31 billion in shareholder value at the world's largest brokerage.

Thain worked at Goldman Sachs for more than 20 years -- in a number of senior executive roles -- before NYSE in 2003 appointed him as its top executive.

At NYSE, he accelerated the Big Board's adoption of electronic trading and converted the nonprofit club into a publicly listed company. And last year, he merged NYSE Group with Euronext to build the first trans-Atlantic exchange operator.

Before joining NYSE, he served as Goldman Sachs Group Inc's president and chief operating officer.