Former New York City Mayor Rudolph Giuliani, who made headlines in the 1980s prosecuting Wall Street financiers, now plans to join the club and build an investment advisory practice.

Giuliani's consulting firm on Wednesday said it purchased accounting firm Ernst & Young's investment banking practice for an undisclosed price.

The new investment bank, Giuliani Capital Advisors LLC (search), will advise companies on deals such as acquisitions and restructurings.

The Ernst & Young investment banking unit, Ernst & Young Corporate Finance LLC, has executives and staff in six U.S. offices.

Steven Oesterle, managing director at Giuliani Partners since Jan. 1, 2003, will be chairman and chief executive officer of Giuliani Capital Advisors. Oesterle is a former vice chairman of Ernst & Young LLP.

This is not Giuliani's first trip to Wall Street

Prior to being the 107th New York mayor and widely praised for his leadership during the Sept. 11, 2001 attacks on New York and outside Washington, Giuliani was U.S. Attorney for the Southern District of New York.

Giuliani led efforts against drug dealers, organized crime, government corruption, and white-collar crime. He is probably best known for his prosecution of Michael Milken (search), the Drexel Burnham Lambert (search) executive who fueled the rise of the junk bond finance market on Wall Street.