Speculation has focused on Laurence Fink, the CEO of Blackrock, and Robert McCann who heads Merrill's brokerage division.

NPR: Merrill Lynch Begins CEO Search

Run by Merrill veteran Robert McCann, a onetime trader who clashed with O'Neal and left for a spell in 2003, the retail group has a 26% pretax margin and earns a healthy 30%-plus return on equity.

FORBES: Magazine Article

Thain also leapfrogged over insiders who had been considered candidates, including Greg Fleming, an investment banker who is Merrill's co-president, and Robert McCann, the head of its brokerage division.

FORBES: Merrill Hires Mr. Fix-It