Tall, lithe and an avid basketball player, Mr. Prokhorov had been publicity shy, mostly confining his appearances outside the boardroom to sports events. Recently, though, he has become a magnet for photographers and fans wanting to shake his hand, and is now something of a dark horse in Russian politics. Mr. Prokhorov made his fortune in metals and mining as co-owner of the world’s largest nickel factory. With serendipitous timing, he sold his stake in 2008 at the peak of the market and entered the global recession mostly in cash. Finans magazine in 2009 estimated his net worth at more than $14 billion. In 2009, Mr. Prokhorov bought the Nets and a stake in the Atlantic Yards development in Brooklyn that will include their team’s new stadium. He has promised to pour some of his personal fortune into the team and apply his business acumen to obtaining players and improving the team’s performance.