Third Point LLC, the hedge-fund firm led by billionaire Daniel Loeb, has become one of Ally Financial Inc.'s largest shareholders as the U.S. government reduces its stake in the company.

Third Point amassed a 9.5 percent stake over the past six months in the Detroit-based auto lender through private transactions, the hedge-fund firm said in a fourth-quarter investor letter dated today. The U.S. Treasury Department last week sold about $3 billion of Ally common stock, reducing taxpayers' stake to 37 percent. The shares aren't publicly traded.

Ally Chief Executive Officer Michael Carpenter has wound down mortgage operations that fueled losses and sold other assets as the lender seeks to exit a $17.2 billion bailout. Last month, the company won Federal Reserve approval to become a financial holding company, allowing it to keep an insurance business and a vehicle-auction website.

"Mr. Carpenter has guided Ally through one of the largest and fastest restructurings we have witnessed," New York-based Third Point said in the letter. The actions "are only the beginning of the story from this team, and we expect them to execute on their multiyear plan to significantly increase Ally's earnings."

The hedge-fund firm expects the U.S. to exit its stake this year, probably through an initial public offering, and the company to achieve a multiple higher than one times book value, "well above the valuation of our purchase levels," according to the letter.

"Ally is pleased to have a diverse group of high-quality investors purchase equity in the company," Gina Proia, a spokeswoman for the lender, said in an e-mailed statement.

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