Maverick Carter heads up SpringHill Entertainment, a multiplatform production company he owns with LeBron James. 

"LeBron and I have always been interested in the long game," said Carter. "And the long game here is to build a media company. To really, truly build a media company."

"Maverick's network is at the highest levels of business in the U.S. and abroad," says Harvard Business School professor Anita Elberse, who published a case study about James and Carter in 2009. "He stands shoulder to shoulder with Steve Ballmer and Bill Gates. And then, in the entertainment world, it's a ridiculous list of movers and shakers."

Carter's inner circle includes their high-powered entertainment agent, Ari Emanuel, the co-CEO of William Morris Endeavor.

"We're still climbing Mount Kilimanjaro," James said. "But having this group of people, who can put together my thoughts and bring them to fruition, is the vision that I had 10-plus years ago."

SpringHill has produced Survivor's Remorse on Starz, The Wall on NBC and Cleveland Hustles on CNBC. SpringHill also owns Uninterrupted, an online network for athlete-centric, nonjournalistic projects.

"LeBron James will have one of the most exciting careers to be a part of for the next two decades," says Paul Telegdy, who oversees The Wall as NBC's president of alternative and reality programming. "Business, entertainment, anything you could apply branding to, he stretches the imagination."

More than a dozen sources directly familiar with SpringHill, including rival producers, filmmakers and media executives, declare James, without debate, the most powerful athlete in entertainment today.