"Most successful people I know are vain," he added. "That's why they're successful. … I don't think there is anything wrong with being vain. If there was, I probably wouldn't admit it."
Trump invited "Nightline" to follow him to his proudest achievement in Manhattan, the appropriately titled Trump World Tower across the street from the United Nations. Trump said the building cost "about $320 million."
While the downturn has affected most of the real estate market, Trump says that high-end properties are still going up in value. We visited a couple who are the owners of a penthouse on the 87th floor whose value has quadrupled in three years.
The kitchen cost "around 140 grand," said the owners.
The owner, who is Greek, added that everyone in her home country is familiar with the name Trump.
But the Trump brand is not welcome everywhere. Trump plans to build two golf courses, a five-star hotel and 900 vacation properties on a strip of land near Aberdeen in Scotland. But the locals don't want the development and the planning application is still awaiting approval. Some of the opponents say the development would damage important wildlife, including seven species of rare birds.
"We disagree with them entirely," Trump said. "And you know the amazing thing is, you're right, there is a group of bird supporters on the site and right now you know what the site is used for? It's a hunting site for birds. … And if I build a golf course all we're gonna shoot is birdies and eagles. I hope we get the approvals. And if we do, it'll be the greatest job of its kind anywhere in the world."
Back in Manhattan, the 61-year-old real estate mogul says he's now a double billionaire. So, as the majority struggle through this period of economic slowdown, what are upsides and downsides of having so much disposable cash?
The Center for Risk Research at the Stockholm School of Economics recently published some research that found "obsession with money or the excessive pursuit of it is really reflective of a deep deficiency of our emotional lives and of our relationships." Trump said he agrees.
"Many people that I know who were the happiest and in many ways, the most secure, are not wealthy. They have a good family, they have a nice wife, they have a nice this, and they're not wealthy. Many of the really wealthy people that I know are insecure, never satisfied, have lots of problems. I don't put myself in that category by the way."
Trump did say that his commitment to business caused him problems in his personal life.
"Look, I've had three marriages," he said. "I've had three nice wives. But in a certain way, I could only speak for the first two — it was very hard for them to compete with my business."
When asked whether he loved his business more than his wives, he said, "I just know it's very hard for them to compete because I do love what I do. I really love it."
Is that why his first two marriages failed?
"Possibly, it's really possible," he said. "You know, you never really know why marriages fail but certainly possibly that's true."
And with that, Trump had to rush off — not to see his wife but another development he's planning in Manhattan.