Steven Rattner has left his high-profile position as deputy chairman of Lazard Freres to start Quadrangle Group, a private investment firm that will focus on the media and communications industries.

Quadrangle said Tuesday that it was aiming to invest in companies at every stage of development.

Rattner will be joined at Quadrangle by three Lazard colleagues. David Tanner was most recently a managing principal and co-head of Lazard Capital Partners, the firm's domestic private equity group; Peter Ezersky was a managing director and head of the worldwide media and communications group, and Joshua Steiner was a managing director in that group.

Former clients of the quartet include

Bertelsmann

,

McCaw Cellular Communications

,

America Online

(AOL)

,

Nextel Communications

(NXTL)

and

Paramount Communications

, a unit of

Viacom

(VIA) - Get Report

.

An advisory board is now being formed. Three of the initial members -- and initial investors -- are Barry Diller, chairman and chief executive of

USA Networks

; Amos Hostetter, a nonexecutive chairman of

AT&T

(T) - Get Report

and the founder of

Continental Cablevision

, and Craig McCaw, the founder of McCaw Cellular.

Other members are likely to include individuals from private equity firms.

To date, Quadrangle has secured $250 million in early commitments and is on track to form a $1 billion fund, according to an industry insider.

Rattner, 47, stepped down as deputy chief executive in July and became deputy chairman after the announcement of the merger of Lazard's three houses -- in London, New York and Paris. That merger is expected to occur next week. The management shift at Lazard was seen as tempering Rattner's ambitions to succeed Lazard's chief executive, Michel David-Weill.

Rattner, who has been an investment banker since 1982, has spent the last 11 years at Lazard. Previously, he was a reporter with

The New York Times

for nine years. He is also an active Democratic Party fund-raiser and the chairman of

Channel 13

, New York's public television station.