Dec 2 (Reuters) - Blackstone Inc (BX.N) told its employees on Thursday that Executive Vice Chairman Hamilton "Tony" James, a key contributor to the firm"s rise to become the world"s largest alternative asset manager, will retire. James, who joined Blackstone in 2002 as president and chief operating officer, led the firm"s initial public offering and the acquisitions of its $178 billion credit business, previously known as GSO, as well as its secondaries arm, Strategic Partners. He also helped establish Blackstone"s $34 billion tactical opportunities division.During his tenure, he helped fundamentally transform and institutionalize the firm," Blackstone Chief Executive Stephen Schwarzman said in a memo to employees. James, 70, handed over his roles as Blackstone president and chief operating officer to Jonathan Gray in 2018. Gray is now heir apparent to Schwarzman. "Tony gave us the gift of time, by beginning the conversation around succession well before his intended exit," Schwarzman said in the memo. Prior to joining Blackstone, James spent more than two decades as an investment banker at Donaldson, Lufkin & Jenrette, which was later acquired by Credit Suisse First Boston in 2000. James is a prominent donor to Democratic candidates. Reuters reported that he turned down an offer in 2012 to join U.S. President Barack Obama"s cabinet as commerce secretary. James sits on the boards of several charities including the Metropolitan Museum of Art, Mount Sinai Hospital System, and Wildlife Conservation Society. He is also board chairman of retailer Costco Wholesale Corporation (COST.O).