New York City ? The unfolding credit crisis has claimed its biggest corporate casualty so far: Merrill Lynch CEO Stan O’Neal.

The announcement of his departure Tuesday came after the world’s largest brokerage posted a $2.24 billion quarterly loss, its biggest since being founded 93 years ago. Merrill Lynch did not name a replacement for O’Neal, whose ouster had been expected, and who leaves the company with benefits worth $161.5 million.

Laurence Fink, the chief executive of investment manager BlackRock Inc., turned down an initial overture from Merrill’s board but is in active negotiations, according to a person with direct knowledge of the offer who was not authorized to speak publicly.