When Ari Emanuel, the 53-year-old co-C.E.O. of the powerhouse talent agency William Morris Endeavor (known as WME), wants something, he doesn't quit until he gets it. Generally seen as the inspiration for Ari Gold, the crass, overbearing talent agent played by Jeremy Piven on the HBO series Entourage, Emanuel is known for in-your-face tactics that are extreme even by Hollywood standards. CBS president and C.E.O. Les Moonves, who describes himself as “definitely a fan” of Emanuel's, says, “He is relentless to the point of ‘Ari, stop calling me. I'll make my decision when I make my decision.’ ” Moonves tells of a recent negotiation over the television show Extant: “We just recently picked it up for a second year, and Ari called me once a day for, like, three weeks. And it was like ‘Ari, I'll tell you when it's ready. I will tell you when I'm ready,’ you know. ‘Well, how are we doing? Are we close? Are we lukewarm? What's the situation?’ ”

For many years Emanuel's most enduring obsession was to combine his talent agency, whose clients include movie and television stars such as Ben Affleck, James Franco, and Oprah Winfrey, with IMG, the sports-entertainment-and-marketing giant that has worked with such elite athletes as Arnold Palmer, Jack Nicklaus, Tiger Woods, Pete Sampras, and Martina Navratilova. Emanuel's quest to own IMG began in earnest in the summer of 2004, when he and others had dinner with private-equity mogul Teddy Forstmann at the fashionable (now defunct) Midtown Manhattan restaurant Davidburke & Donatella, according to a former Forstmann partner. The two men discussed how Forstmann's firm, Forstmann Little & Company, might make an investment in Emanuel's agency, Endeavor, as it was called before it merged with William Morris. A term sheet was drawn up, but the deal went nowhere.

Forstmann—himself a larger-than-life character, just as passionate and mercurial as Emanuel—also nursed an obsession to own IMG, which was then still controlled by its founder, Mark McCormack. An amateur golf player, McCormack had begun the firm to help his friend Arnold Palmer and other professional athletes earn extra money by endorsing products and adding their star power to corporate marketing campaigns. Forstmann thought IMG was amateurishly run but full of potential. “They had a hell of a franchise that they weren't really taking advantage of,” he told me in a December 2010 interview in his posh office in Manhattan's G.M. Building. “This company had never used the word ‘profit.’ Mark liked to end the year at zero. He wanted to take the last $20 or $25 million. None of these people knew what the other guy did. It was … I'll use colorful language … It was the most fucked-up company I've ever seen in my whole life by a long shot.”

McCormack had no desire to sell, however. “How I got the deal was he died,” recalled Forstmann bluntly. During Forstmann's negotiations with McCormack's estate, Forstmann and Emanuel kept talking, and before Forstmann closed the deal, for $750 million in cash, in November 2004, the two men considered the possibility of IMG's also acquiring Endeavor, with Emanuel running the combined company. When that did not come to pass either, an incredulous Emanuel is said by a Forstmann insider to have proclaimed that the merger would be happening and that he was, in fact, going to be the C.E.O. of the combined company. Such exuberance left Forstmann nonplussed and a bit miffed.

Over the next decade Forstmann transformed IMG into an international production-and-packaging powerhouse. The expanding business cut profitable deals with more than 200 American college and university sports teams, as well as with Indian Premier League cricket, Wimbledon, the Australian and U.S. Open tennis tournaments, tennis tournaments in Spain and Malaysia, and Barclays Premier League soccer. It ran Fashion Week in New York, Milan, and London, and in China it formed an exclusive joint venture with the national television network to create sports programming—all this in addition to representing such sports stars as Novak Djokovic, Maria Sharapova, and Venus Williams. It also signed up an array of fashion designers and models, including Michael Kors, Diane von Furstenberg, Gisele Bündchen, and Kate Moss.