Brian Duperreault was named president and CEO of Marsh & McLennan Cos. Inc., effective immediately, confirmed spokeswoman Celeste Martinez. He replaces Michael G. Cherkasky, who stepped down in December. Mr. Duperreault was CEO of ACE Ltd. from 1994 to 2004 and chairman of the board from 2004 to 2007; he was a director until todays appointment. Evan G. Greenberg, CEO of ACE, was named chairman in May, according to the companys website. MMC is the parent company of investment consultant Mercer.