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Who

Ira Rennert is known for two things: the vast wealth he's acquired thanks to investments in highly unpopular industries, and his home in the Hamptons, which has the distinction of being the largest residential structure in the country.

Backstory

Rennert started off working on Wall Street, but he didn't stay there long. He was censured by the NASD on several occasions in the early 1960s and had his license revoked in 1964, a move that effectively banned him from working in the securities industry. Undeterred, the Brooklyn-born investor moved on to the unregulated world of private equity, amassing a collection of unpopular businesses in the 1970s and 1980s through his holding company, Renco. Often using junk bonds to finance his steel, magnesium, coal, and lead companies, Rennert made more than a billion dollars over the years, but clouds of controversy have always hovered overhead. A number of his companies have gone bankrupt leaving creditors and bondholders in the lurch, and he's amassed a contentious environmental record—an issue that led to a $900 million fine in 2001. (Rennert managed to avoid paying the staggering amount by sending the subsidiary involved in the alleged toxic dumping dispute into bankruptcy.) More recently, he's created an uproar in Peru, where one of Renco's facilities is believed to be responsible for widespread environmental damage.

Rennert may be best known, though, for purchasing AM General, the not-so-environmentally-friendly company that manufactures the Hummer SUV and Humvee military vehicles. He bought the company for $133 million in 1992 by putting down just $10 million in cash; he hit the mother lode in 2004 when he sold a 70 percent stake to Ron Perelman's MacAndrews & Forbes for close to $1 billion.

Keeping Score

In 2008, Forbes pegged Rennert's net worth at $6.0 billion.

Habitat

In 1994, Rennert picked up a 63-acre oceanfront parcel in Sagaponack that he dubbed "Fair Field." In 1998, construction began on a 66,395-square-foot Italianate mansion with 29 bedrooms, 39 bathrooms, and a staff wing; the $100 million project also included a 17,000-square-foot garage (large enough to fit more than 100 cars), gym, lounge, game room, basketball court, handball court, billiard room, two indoor tennis courts, and playhouse with two bowling alleys. Not surprisingly, when the plans were revealed, nearby residents were outraged and sued to stop the town from issuing building permits, arguing that Rennert planned to use it as a community center or even a synagogue, a violation of local zoning laws. (Rennert is a religious Jew.) He ended up prevailing and moved into the home in 2004. He also owns a $6 million pied-a-terre at 625 Park Avenue and a house in Israel, which he travels to aboard his Gulfstream V jet.

Pet causes

Rennert describes himself as an Orthodox Jew and as such, he gives to Jewish causes in both the U.S. and Israel. The president of the Fifth Avenue Synagogue, he contributed $2.5 million to establish a chair in Jewish studies at Barnard several years ago, and he donated some $5 million to establish the Elie Wiesel Center for Judaic Studies.

Personal

Rennert and his wife, Ingeborg, have three kids: Yonina ("Nina") Rennert Davison, Tamara Rennert Winn, and a son named Ari, who is a vice president at Renco. Luckily for the Rennert offspring, Ira insists that his children live in quarters no less lavish than he'd deign to live in himself. He recently bought Tamara a duplex at 740 Park for $32 million and Nina a 14-room apartment at 778 Park (that previously belonged to Vera Wang) for $33.6 million.

No joke

The assessed value of the Sagaponack property in 2005? A mere $170,167,400.