On the day after he retired as a major leaguer — following 21 seasons with the Baltimore Orioles, nearly 12,000 trips to the batter’s box, and a legendary 17-year streak without missing a game — Cal Ripken Jr. says he had to “take the baseball uniform off, put a suit on, and go to work.”

Thirteen years later, it’s hard to come up with a one- or two-word description for that job: “shortstop,” “third baseman,” “slugger” — none of those applies anymore. But Ripken can manage it in three: It’s the “business of Cal,” says the 53-year-old Hall of Famer. Ripken had the foresight to start planning early, before the end of a pro career that made him some $70 million in salary (low for a star by today’s mega-contract standards). “When you’re playing, you’re making contacts, you’re meeting people all over the place,” he says. “I always thought, Take advantage of those contacts to start to set up your post-career.” And today the business of Cal is bustling.

His privately held company, Ripken Baseball, operates two youth-oriented complexes, both called Ripken Experiences: a huge one in Aberdeen, Md., sponsored by Under Armour, that puts on weekend-long kids’ tournaments and camps with replica fields modeled after current parks like Fenway and Wrigley, and one in Myrtle Beach, S.C., that offers weeklong tournaments on fields that mimic historic parks like Ebbets Field. Both are growing fast enough that Ripken’s next step is to duplicate the experiences across the U.S.

Ripken hasn’t always batted a thousand in business. At first he focused on minor league baseball. In 2001, just after retiring, he purchased a Utica, N.Y., team for some $3 million and moved it to Aberdeen, his hometown, renaming the team the Aberdeen IronBirds. In the process, he helped negotiate a public-private partnership for the completion of a $21 million stadium project. He kept buying: In 2005 he purchased the Augusta GreenJackets, and in 2008 the Charlotte StoneCrabs. But in 2012 he sold off the GreenJackets (for a reported $7.5 million) and sounds unlikely to buy a team again.

Minor league ownership, he says, is thorny with politics and zoning issues. “We had immediate success with [the IronBirds], and I assumed that success could be applied everywhere,” he says. “But I think, in hindsight, we got diverted toward minor league teams. The future for us is in youth complexes and tournaments.”

The Ripken Experience in Aberdeen is populated with kids every weekend from March through Thanksgiving. (Ripken has a small equity stake in a big Marriott hotel on the site.) And the complex at Myrtle Beach has been a lure to family vacationers.

Endorsement deals with Kellogg’s and other companies, part-time baseball broadcasting for TBS, and speeches that fetch $50,000 a pop bring in a few more million per year to the business of Cal. But the youth complexes are something the 19-time All-Star hopes he can build on. “We run tournaments very well, and we’re selling tournaments very well,” he says. “As that starts to grow, the model doesn’t have to have me in the equation.”

As Cal’s brother and business partner Bill Ripken puts it, “He’s always going to be that guy — the Iron Man. But 50 years from now, when that guy might be gone, the complexes will still be running strong.”

WATCH: Cal Ripken on the big business of baseball

This story is from the May 19, 2014 issue of Fortune.