(FORTUNE Magazine) – WHAT DRIVES Michael Milken? ''Mike believes in 100% market share,'' says John H. Kissick, head of Drexel Burnham's corporate finance department in California. Observes raider Irwin Jacobs, who raised $300 million through Milken: ''He's aggressive, the way he hustles business. He won't let you live if he smells you're thinking of going somewhere else for financing. Then he's on the phone, trying to make a deal.'' Being in charge has been almost a way of life for Milken, 42. Even at Birmingham High School in Van Nuys, a prosperous Los Angeles suburb, he dominated several of the organizations he joined. He was head cheerleader in 1964 and even king of the senior prom. As a college student -- a business major at Berkeley -- Milken was elected head of his pledge group and then, in his senior year, president of the fraternity. This was not because of any spontaneous outpouring of support from his peers. ''I don't think you would say he was popular in the fraternity,'' says fratmate Jeffrey Unickel, later an usher at Milken's wedding. ''It wasn't charisma. He campaigned very hard and gathered people's respect. It was like running for political office -- kind of Machiavellian. He worked at it. He was as driven to succeed as anybody.'' Virtually a straight-A student, Milken was also elected to Phi Beta Kappa. His financial shrewdness and abundant energy were already apparent in college. ''Mike has always gotten by on three or four hours sleep,'' says Harry Horowitz, his best friend since grammar school and now a Drexel senior vice president. At Berkeley, Milken played cards all night long: ''There was a semester-long poker game,'' recalls a fraternity brother. ''I remember he was down one time by maybe a thousand dollars -- that was an astounding amount in those days. But he didn't care. He was the house -- the one taking all the bets. He knew the odds were in his favor and that he'd get his money back.'' At sunrise Milken would quit playing cards and go down to a stockbroker's office on Shattuck Avenue to watch the stock market. The son of an accountant, he already had a sharp eye for a deal. ''He invested in a computer software company that made a program for accountants,'' says Unickel. ''He discovered ! the company when he was doing work for his father. I coattailed with him on the stock -- buying and selling when he did. We did quite well.'' Says the fraternity brother: ''He was monomaniacal about making money. To be a millionaire by age 30 was his goal. I thought I shared the same goal, but Mike was different. He wanted to be rich.'' AFTER GRADUATING from Berkeley in 1968, Milken married Lori Hackel, his girlfriend since high school, then headed east to Pennsylvania's Wharton School for an MBA. There he studied the default rates and yields on junk bonds, discovering they were less risky than most people thought. Says finance professor James E. Walter, who helped him: ''He worked on it. It wasn't an intuitive flash.'' In 1973 Walter and Milken co-authored an arcane 46-page paper titled ''Managing the Corporate Financial Structure.'' Milken delivered it at a Financial Management Association conference that year. By then Milken was going to school part time while working in Philadelphia at Drexel Firestone, one of the forerunners of Drexel Burnham Lambert. (He didn't get his MBA from Wharton until 1978.) His first job at Drexel was attacking the back-office crunch plaguing most brokerage houses at the time. Recalls Ernest Widmann, then Drexel's co-director of research: ''He was an operations research major at Wharton, using mathematics to solve all kinds of organizational or business problems.'' Milken hardly made the problems disappear, says Widmann, but offered several down-to-earth, nonmathematical solutions. Widmann remembers Milken wandering into his office to discuss junk bond theories late at night: ''He was very focused. He was affable, but he had his own agenda. There was no small talk.'' Eventually Milken was given a corner in the bond trading department, where he could begin to sell his ideas. ''He was brilliant,'' says Widmann, ''but he wasn't the typical egghead. He could talk to clients without scaring them.'' In the mid-1970s Milken, eager to spread his junk bond heresy, found an enthusiastic ally in Meshulam Riklis, chairman of Rapid-American Corp., a conglomerate put together with vast quantities of junk-rated debt. ''At the time I was about the only person using high-yield bonds to make acquisitions,'' says Riklis. Milken enlisted Riklis to appear before groups of skeptical bond buyers. ''He wanted me to show why my company was highly leveraged and still highly profitable.'' At first Milken peddled the bonds of so-called fallen angels, companies ^ whose bonds were gilt-edged when first issued but slipped below investment grade later. By the late 1970s other brokerages tried floating corporate bonds that were low rated from the first. Conservative institutional investors avoided them, but soon Milken was pushing them to a growing network of devotees. In effect, Milken kept the entire market in his head. ''His memory is tremendous,'' says Riklis. ''He was interested in hundreds of bonds and could remember and advise his customers on all of them.'' Milken was on the phone constantly, lining up buyers and sellers. With yields two, three, even four percentage points higher than top-quality bonds, business boomed. Says Riklis: ''Mike could sell it so well, he had to go out and create more of the product.'' Drexel encouraged companies to issue the stuff. Between 1978 and 1983 the junk market grew mightily. Milken prevailed on Drexel Burnham to let him move his operations to California in 1978. The father of two sons and a daughter, he wanted to put in a long day and still get home in time to be with his family. He bought a $675,000 home on nearly an acre in the Encino hills, where the rich kids from Birmingham High used to live. Milken still arrives at the office by 5 a.m., but leaves evidence of having been up working even earlier. Often when his staff comes in they find each desk plastered with a half-dozen notes, reminders, and follow-ups. ''Sometimes there are 300 notes,'' says one observer. MILKEN'S TRADING STYLE is fast paced -- he sits at the center of an X-shaped group of desks, surrounded by colleagues. ''Everybody would be yelling at him,'' says a former Drexel bond buyer. ''He'd be holding six conversations at once -- two on the phone, three across the room, and with me. I'd have to try to figure out when he was talking to me.'' Corporate executives and other visitors trying to do business with Milken are not treated any more gracefully, and may be told to meet him at 6 a.m. Meshulam Riklis finds, however, that Milken can be accommodating: ''I'm too old to get up that early,'' says the 64-year-old executive. So Riklis rides with Milken when he takes his Mercedes back to Encino in the evening. Following close behind is Riklis's chauffeur-driven car, to bring him back to Los Angeles. Businessmen energetic enough to meet with him come away impressed with his smarts and creativity. But Milken doesn't respond well to teasing about a deal gone bad. He heard once that a Los Angeles firm, Froley Revy Investment Co., as part of its annual roast had given an award tongue-in-cheek to a Drexel bond that dropped in price soon after it was issued. Milken had one of his brokers call the firm and point out that bonds issued by other underwriters had fared worse. ''I was impressed by his attention to detail,'' says Thomas Revy, a partner at the investment firm, ''but not with his sense of humor.''