The Hershey Trust manages $8 billion in assets owned by the Milton S. Hershey School for underprivileged children. Among the school's assets is stock that controls the Hershey Co., the chocolate-bar-maker and major Pennsylvania employer, and the Hershey amusement park.

As president of the trust in 2002, Vowler played a central role in negotiating to sell the Hershey Co. to diversify the multibillion-dollar school endowment. But the deal encountered fierce community opposition and fell apart. Company and trust officials revived deal talks in 2007, again without success.

Vowler, 53, said yesterday in a phone interview: "I'm still a young man, and it's a good time to move on." He said he was grateful the trust board offered him early retirement.

The trust has partially diversified the school's endowment, he said, estimating that 40 percent of the school's endowment is locked up in Hershey Co. stock.

Vowler was president and chief executive officer for 12 years and was set to retire in April 2009, serving as an adviser to the trust until then. "Helping to lead the preservation and advancement of Milton Hershey's ongoing philanthropy has been the privilege of a lifetime," he said in a statement.

Critics say the Hershey School, which educates lower-income children in kindergarten through high school, is too exposed to the fortunes of the mass-market chocolate company that is facing shifting consumer tastes and slow growth in the United States. Hershey failed to match the overseas expansion of its arch-rival Mars Corp., the maker of M&Ms and Snickers, they say.

The most powerful official among the Hershey profit and nonprofit entities is LeRoy Zimmerman, a former Pennsylvania attorney general and chairman of the Hershey Trust Co. and Hershey School board of managers.

Zimmerman has said he believed the Hershey Co. should keep its headquarters in Pennsylvania and has indicated that the company should seek deals to expand into international markets.

Some experts question whether the Hershey bar, which chocolate gourmands say has a bitter taste, would do well overseas. Hershey's also owns the Reese's peanut-butter cup, Fifth Avenue, Zagnut, York Peppermint Pattie and other candy brands.

Higher prices for milk and other commodities have cut into Hershey's profit margins. It is closing plants and relocating candy production to Mexico. Chief executive officer Richard Lenny was ousted last year.

Vowler said his own departure was "totally unrelated" to Lenny's.

"We are grateful to Rob for his service and grateful to him for the methodical and prudent manner in which we will implement his retirement," Zimmerman said yesterday in the statement.

The profiles of two executives in the Hershey Trust will be elevated with Vowler's departure. They are Vincent B. Rudisill, chief investment officer, who will be executive of the trust, and Andrew G. Keefer, who will serve as interim executive of the trust services to individual and institutional investors. The Hershey Trust provides financial services for private clients, along with its management of the school endowment.