Jed Walentas is betting big on Brooklyn.

“This is a once-in-a-lifetime opportunity,” he said. “It’s a sensational opportunity. Brooklyn is going to explode.”

The Walentas bet began 24 years ago as a relatively small wager – at least as far as real estate deals go – when Jed’s father, veteran developer David, bought 2.5 million square feet in a largely decrepit industrial area known as Dumbo, or Down Under the Manhattan Bridge Overpass. He paid $12 million.

Mr. Walentas is, of course, pleased that his only child now manages DUMBO. Jed Walentas, who is in his early 30s, also runs their privately held company, Two Trees Management, on a day-to-day basis. By the time Jed completes the company’s projects in DUMBO, and also the regeneration of large parts of nearby Downtown Brooklyn – in about five years – the Walentases will have spent some $500 million.

It’s a safe guess that David Walentas’s original investment – in which Leonard and Ronald Lauder were partners – has already been recouped, probably several times over. Many of the 1,000 or so apartments that Jed is creating in the converted industrial buildings command more than $800 a square foot.

Some of those buildings date back to the late 19th century, when DUMBO was bustling with commercial and industrial activity.

“Any great neighborhood in the world always has intersections of lots of forces, tastes, cultures, and preferences,” Jed Walentas said. “My father invented the modern DUMBO, and I’m building on what he started. This is an evolving neighborhood, but our imprint will be here for a very long time.”

That imprint, which has already transformed DUMBO into one of the city’s most vibrant neighborhoods, took shape in a time of much frustration and anxiety. David Walentas spent 17 years trying to convince the city to rezone the area for residential uses. Mayor Giuliani was instrumental in pushing through the rezoning in 1997.

By that time, Jed Walentas had graduated from the University of Pennsylvania, with a degree in economics. But neither economics nor real estate were where his true interests lay. It was in writing sports. He was sports editor of the campus news paper, the Daily Pennsylvanian. A job as a sportswriter awaited him at the New York Post.

“I decided to go with Donald instead,” Mr. Walentas said.

“Donald,” of course, was Donald Trump, who was so taken with Mr. Walentas’s enthusiasm and ability to learn quickly that he assigned him to a prime property the Trump Organization was developing. The building was 40 Wall St., which was the first commercial building in New York to be fully wired for the Internet. Jed Walentas supervised much of the construction.

Then came a call from his father. David Walentas thought he was now in a position to carry out his plans for DUMBO, a waterfront area between the Brooklyn and Manhattan bridges. A Scottish immigrant businessman named Robert Gair had built industrial structures there, including cardboard-box factories that made a fortune for him. The area was often referred to as Gairville.

But the neighborhood had deteriorated since Gair’s time. There were artists squatting in abandoned units. DUMBO’s dark and winding streets were sometimes used by mobsters to dump the bodies of people they didn’t get along with.

The Walentases’ first conversion project in DUMBO was the Clock Tower Building at 1 Main St. They built 124 luxury condominiums in the 250,000-square-foot structure in less than a year. They raised a new 12-story building containing 54 apartments. They assembled 200 high-class apartments in three vacant loft buildings. And they upgraded 1 million square feet for artists’ studios and commercial offices.

A lucky streak came along. Stratospheric prices in Manhattan were forcing New Yorkers to look elsewhere; DUMBO’s neighbor, Brooklyn Heights, had regained its long-vanished residential glory, but property prices were edging upward to Manhattan levels.

A buzz developed about DUMBO. The celebrated chocolatier Jacques Torres opened a store-cum-factory. Laudatory articles appeared in trade publications.

And DUMBO was on its way to becoming an urban legend.

That status most certainly will be burnished as a waterfront park opens. Mr. Walentas is convinced that through the peculiar but intangible process by which people from different parts of the city relate to one another, DUMBO will “connect” to downtown Manhattan, which officials also want to develop further.

So what has it been like to generate that connection, beyond the long hours and the daily administrative burdens of running a real estate company in New York?

“It takes patience,” Mr. Walentas said. “It takes long-term commitment to revive a neighborhood. Of course, it takes capital – and here we’ve been fortunate.

” And it takes a certain kind of dedication to the belief that the architecture of a historic neighborhood should be preserved in all its variety. I think we’ve done that,” he said. “There’s a sense of satisfaction and accomplishment in that.”