Perhaps this explains those late-night consultations with Madonna?

New York Yankees slugger Alex Rodriguez has signed with the Hollywood talent agency William Morris, Matthew Futterman of the Wall Street Journal reports.

The deal, the terms of which were not disclosed, underscores how sports stars have become celebrities as big as—if not bigger than—Hollywood and TV stars. And athletes are doing more than product endorsements.

Of course, that has been obvious for several decades, ever since Michael Jordan revolutionized the idea of an athlete as a brand and made 23 a nearly sacred number.

A-Rod clearly has room to do better on the nonbaseball-income front. He has a 10-year contract with the Yankees worth $275 million. But Sports Illustrated estimates that he will receive just $6 million in endorsements this year.

"A-Rod needs a steady hand to manage all aspects of how he is positioned within and beyond baseball," David Carter, executive director of the Sports Business Institute at the University of Southern California, told Bloomberg News. "William Morris delivers that steadiness, as well as a deep set of relationships with corporate America."

Scott Boras, whom Rodriguez did an end run on when the agent announced during the World Series last fall that his client would opt out of his Yankees contract, will continue to handle A-Rod's baseball matters.

The star potential of the Yankees' third baseman is huge. Destined for the Hall of Fame, he is well on his way toward eventually overtaking Barry Bonds as baseball's all-time slugger. He is a handsome man who is always pleasant in public.

But there are also negative factors for any marketer. His wife is divorcing him amid tabloid stories about a relationship with Madonna. And perversely, despite all his attributes and his extraordinary record, A-Rod is not universally loved by baseball fans.

Even many Yankee fans see A-Rod as a cold, aloof star compared with the clutch team captain Derek Jeter. How do you translate that into marketing prowess?

That is the challenge for William Morris, which has an expanding sports roster that includes Michelle Wie, Serena Williams, and Kevin Garnett of the Boston Celtics.