Steven Rattner, deputy chairman at Lazard, is leaving the world's largest investment banking partnership to form his own firm with three other Lazard executives.

Rattner along with David Tanner, co-head of Lazard equity partners, Peter Ezersky, head of Lazard's global media and Joshua Steiner, managing director of the media group, have formed Quadrangle Group, a private investment firm that will specialize in the media and communication industries.