When I first met Nicolas Berggruen, I was struck by two things. First, he was a multi-billionaire I'd never heard of -- the most interesting kind. Second, he didn't own a home.

"I stay in hotels," he told me.

A billionaire without a home? This, I figured, was worth a story. My article about Mr. Berggruen in today's Journal focuses mainly on his investing life and his push toward socially responsible investing. But what interested me most was his unconventional personal life.

After making his billions, Mr. Berggruen, 46, lost interest in acquiring things: They didn't satisfy him, and in fact had become something of a burden. So he started paring down his material life, selling off his condo in New York, his mansion in Florida and his only car. He hatched plans to leave his fortune to charity and his art collection to a new museum in Berlin.

For him, wealth is about lasting impact, not stuff.