"Ryan is really much smarter than he appears to be," his father, Jack, says one brisk January evening, grinning at his elder son across the vast dining room table at the family's home in L.A.'s wealthy Brentwood. Ryan's mother, Leslie, who shares his red hair and his personal trainer, has already pried the BlackBerrys away from her husband and son. As a uniformed server offers a basket of cheese crostini, the talk turns to Ryan's upbringing. It is time to tell the piggy bank story.

Once upon a time, when Ryan was six years old, he saved $57.94. His father instructed him to read the stock tables and list his preferred stocks and his reasons for choosing them in a notebook. Then he took the first-grader to see a stockbroker in Beverly Hills. Ryan bought single shares of Amgen, I.T.T., Citicorp, and a few others. The dividends were reinvested year after year. When Ryan turned 16, the account was worth more than $24,000.

Soon after, young Ryan started several businesses. He put vending machines in the office where his mom worked as a real estate agent. He also teamed up with a partner licensed to sell pepper spray, which he hawked to his mom's friends. Around the same time, Ryan took his $24,000 and tore through it. "I went on a lot of dates," he says.

Kavanaugh says he has two role models: Kirk Kerkorian, the billionaire wheeler-dealer, and his own father. Of the two, the elder Kavanaugh may be the harder act to follow.

Son: He speaks six languages.

Dad: Nine.

Son: He used to work out with Lou Ferrigno. Dad bench-pressed 545.

Dad: 565.

Son: He was extreme skiing and fractured his leg. Now it's a half-inch shorter than the other.

Dad: One and a half inches.

Like any family, the Kavanaughs have many favorite stories. There's the one about Ryan's paternal grandfather, a Polish immigrant who worked as a steel-press operator for 40 cents an hour and changed the family surname from Koniacpulski to Konitz. Then there's the one about Ryan's dad—who'd changed his name to Kavanaugh—breaking his neck. He didn't realize it for months because his overdeveloped muscles held his head up. And there's the one in which Ryan's dad, forced to abandon a dentistry practice because of that same neck injury, got his M.B.A. and became a partner at an investment firm, then in his forties got his M.D. and started teaching eye surgery.

"Jack went through a lot of changes, ups and downs," says Ryan's mom. "And Ryan saw that."

No wonder that, with this family history, Ryan's most staggering setback is told as a tale of perseverance.

This story opens at the University of California at Santa Barbara, where Ryan studied very little, pierced his ears (one of them twice), joined a band called Shades of Grey, and resolved to play guitar for a living. Dismayed, his father promised to never nag his son again if he would cut his shoulder-length hair and take a summer internship at the brokerage firm Dean Witter Reynolds. Reluctantly, Ryan agreed. The decision, he says, "changed everything." By summer's end, Dean Witter offered Ryan a full-time job. He took it and transferred to U.C.L.A. (where he is still eight credits short of a diploma). But just months later, at the end of 1996, he left the job to start his own venture capital firm. He asked his dad for a $50,000 loan but was turned down.

"Who's going to give a 22-year-old any money?" Ryan's father asked. The answer, it turned out, was lots of people. Ryan's first investors were college friends. But then he signed up the producer Jon Peters, for whom Ryan's uncle had done some construction work, and Hollywood's doors flew open. Peters was soon joined by Terry Semel, then co-chairman of Warner Bros.; Jonathan Dolgen, then chairman of Viacom Entertainment; and producer Jerry Bruckheimer.