(FORTUNE Magazine) – So you've founded a business, sold it five years later for $250 million, become president of the merged company, and in another five years helped to more than quintuple its sales to $5.3 billion. What's next? If you're Mark Begelman, who pioneered the office-superstore concept with Office Club in 1986 and became president of Office Depot in 1991, you wake up from a decade of nonstop work. You realize that you have 37,000 employees and that your life consists of staples and paper clips. All of which was an unpleasant shock to someone who thinks of himself as a musician. "I was president by day and rocker by night. I wanted to be rocker by day and rocker by night," says Begelman. In 1995 he quit.

With his longish hair, faded black jeans, and unposh office filled with rock memorabilia, Begelman comes across as someone who stumbled into corporate America during a brief delusional spell. In fact, he's as ambitious and aggressive as any more conventional corporate titan. It took Begelman just a few months to tire of strumming his guitar on the beach and to decide to re-create the Office Depot concept--in his industry. What about a chain of music superstores?

Putting theory into action, in late 1995 Begelman bought a struggling chain of South Florida stores called Ace Music. He made connections with vendors, then began closing the small, old Ace stores. In March 1997 he opened his idea of what a music store should be--MARS, or Music and Recording Superstore. (He also changed the name of his band from the Eraserheads to the Men from Mars.) The Fort Lauderdale MARS, which occupies 38,000 square feet in the MARS shopping center, is stocked with all the major categories of musical instruments (except acoustic pianos and church organs). If you find it at a lower price elsewhere, MARS will refund the difference. There's also sheet music, recording gear, a studio, a live stage, and classrooms for lessons--but no tapes or CDs, a market already crowded with superstores. The staff are all musicians--in fact, one of the instructors toured with the Commodores. Browsers are encouraged to jam. "We love when you touch the stuff" is the MARS tag line. Begelman says that more than half his customers are new to music, but serious rockers like Eddie Van Halen, ZZ Top, and Eric Clapton also shop at MARS, and it is supplying the Billy Joel tour.

So far, the formula seems to be working. Begelman has opened 22 MARS stores, from Florida to Texas to Ohio. In 1998, MARS had around $110 million in revenues; Begelman guesses the 33 stores he'll have by year-end will generate more $200 million and that MARS will become profitable in the fourth quarter of this year. MARS has raised $100 million in private financing, and Begelman talks about going public as early as 2000.

Begelman's goal is audacious: He wants MARS to be a music store category killer, to be the next Home Depot or Wal-Mart. There are more than 8,000 specialized music and sound retailers, mostly mom-and-pop stores, which sold $6 billion of gear in 1998, according to the National Association of Music Merchants. The industry has grown 7% a year this decade, and Begelman has lots of ideas about how to speed that rate up. For example, he seems to have tapped into baby-boomer yearnings with innovative programs like Rock U, which offers graying pupils rehearsal space, gear, even other musicians.

Still, no matter how many 50-year-olds want to reconnect with their rock-star fantasy selves, Begelman's dream won't come easy. The $6 billion that shoppers spend on music each year is less than 4% of the $185 billion that they spend on those mundane office supplies. (You don't run out of drums.) MARS is hardly a low-risk proposition: Each store costs $2.8 million, and there is competition, like Guitar Center and privately held Sam Ash. But Begelman is confident. "Thanks to Office Depot, there isn't a transaction in retail I don't know, except for Chapter 11," he says, "and I'll pass on that bad boy."

--Bethany McLean