Theodore J. Forstmann has been in many corporate battles over the past four decades as one of Wall Street’s premier deal makers, but now he finds himself in what may be the biggest battle of his life.

People close to Forstmann confirm to the FOX Business Network that Forstmann is undergoing treatment for brain cancer. These people confirm that Forstmann recently underwent brain surgery to remove a malignant tumor, though he is recovering, and according to people close to him, he has returned to work managing his private equity firm, Forstmann Little & Co.

Through a spokeswoman, Forstmann, 71, declined to comment. But friends who have seen him in recent days say Forstmann is optimistic about his chances for recovery, and he has been seen out and about at his favorite Manhattan restaurants.

Forstmann Little has acquired 31 companies over the years. He currently owns the sports, media and entertainment company IMG, which manages prominent clients including Tiger Woods and the model Heidi Klum. 

Forstmann has a net worth of approximately $1.6 billion, according to Forbes, and even while recovering from surgery has been actively running IMG. Forstmann has also been romantically linked to actress and model Padma Lakshmi.

For all of his business success, Forstmann may be best known for a deal he didn’t win. In the 1980s he attempted to take over RJR Nabisco, but ultimately lost out to his long-time nemesis, Henry Kravis, who used high-yielding “junk bonds” to finance the acquisition. Forstmann became a loud critic of using junk bonds to finance takeovers, calling them “funny money” and “wampum” and correctly forecasting the market crash and recession that emerged after the debt-fueled takeover binge of the 1980s.

Charles Gasparino joined FOX Business Network (FBN) in February 2010 as Senior Correspondent.