American International Group Inc., the world’s biggest insurer, ousted its chief executive officer Martin Sullivan after record losses, a sagging stock price and criticism from the leader he succeeded in 2005, Maurice “Hank” Greenberg.

Robert Willumstad, 62, chairman of New York-based AIG, adds the CEO title, the insurer said yesterday in a statement. Mr. Willumstad called AIG’s two record quarterly losses “unacceptable” and promised a “thorough” review of strategy and operations.

“Nothing is off the table,” Mr. Willumstad said in an interview. “I’ve set a goal in the next 90 days to dig into the businesses, all of the businesses, not just the non-insurance businesses, to make sure our capital is being employed in the right areas.”

Mr. Sullivan becomes part of a CEO exodus from companies including Citigroup Inc., Merrill Lynch & Co., and Wachovia Corp. that underestimated how badly their profits would be hurt by the collapse of the American subprime mortgage market. AIG posted more than $13 billion in losses in recent quarters, after Mr. Sullivan assured investors in December that any drop in the value of its holdings would be “manageable.”

The chairman of KB Home and former CEO of Hilton Hotels Corp. who serves on AIG’s board, Stephen Bollenbach, 65, will be the lead independent director, the company said.

Investors including Greenberg and Legg Mason Inc.’s Bill Miller demanded a new chief after AIG, ranked no. 1 by assets among insurers, lost 46% of its market value since Mr. Sullivan took the top job. Calls to Mr. Sullivan for comment weren’t answered.