He has given more money to conservation causes in California than anyone else. His gifts have helped protect 1,179 square miles of mountain and desert landscapes, an area the size of Yosemite National Park.
His donations to wilderness education programs have made it possible for 437,000 inner-city schoolchildren to visit the mountains, the desert or the beach -- often for the first time.
Over a decade of steadily growing contributions -- including more than $100 million to the Sierra Club -- this mathematician turned financial angel has taken great pains to remain anonymous.
In manner and appearance, David Gelbaum has maintained a low profile for someone who can afford to give away hundreds of millions of dollars.
At age 55, retired from the rarefied world of Wall Street hedge funds, he lives in Newport Beach with his wife and two of his five children in a large home where visitors on occasion have mistaken him for the gardener. Bespectacled, 5 feet 5 and slightly built, he speaks softly, barely above a hoarse whisper. He drives a Honda Civic hybrid, wears jeans and T-shirts to business meetings and helps the kids clean up at the wilderness camp-outs he sponsors.
Those who know him say he is never more uncomfortable than when asked to talk about his wealth or how much of it he has given away.
His donations, which according to public records and other sources total at least $250 million, have preserved hundreds of miles of wildlife corridors across mountains and deserts, tying together once-isolated national parks and wilderness areas. One conservation deal, land trust experts say, is the largest single purchase of private land ever handed over to the U.S. government for one purpose: to leave it alone.
He has given more than $20 million to schools in Orange County and handed over 108 rolling acres in the foothills of the Santa Ana Mountains for use as an outdoor-education camp.
He has contributed $3.5 million to Orange County Sheriff Michael S. Carona's foundation to help the poorest children attend the camp's wilderness programs. Carona is both grateful and a bit mystified by the benefactor.
"He's one of these strange guys who doesn't want any publicity but wants to take care of kids and the community," Carona said. "When you look him in the eye and say, 'You've made a positive change in these kids' lives,' he does not want to take any credit for it. He's almost embarrassed when you say thank you to him."
(A federal grand jury recently subpoenaed financial records of Carona's foundation. Federal officials have not disclosed why they want the documents.)
Gelbaum, a native of Minnesota who moved to California as a teenager, was a math prodigy who parlayed his talents into a highly lucrative three-decade career using mathematical formulas to pick stocks and bonds for wealthy investors in hedge funds.
He won't say how much he made. He started giving his money away in ever-larger amounts in 1994.
"Most wealthy people spend their lives trying to make more and more money rather than give it away," Gelbaum said during a series of interviews that he agreed to only reluctantly. "They wait too long. They are depriving themselves of a lot of joy. I'm doing what I want to do. It's not like it's money that I or my family will ever need.
"It's a joy to see this land preserved and opening these kids' eyes to the natural world. It's not like burning the money. It goes into the land or into the kids' experiences. Both last forever."
Some charitable foundations have given more money to conservation causes, but much of it is aimed at saving tropical rain forests or other overseas ventures. The only individual whose contributions to California conservation rival Gelbaum's is Caroline Getty, granddaughter of oil tycoon J. Paul Getty. She recently donated $150 million to the Preserving Wild California project of the Resources Legacy Fund Foundation.
Gelbaum said his interest in land conservation was inspired by camping trips he took with his father and brothers to lakes in northern Minnesota, as well as Yellowstone National Park and Mt. Whitney. "Those were the happiest memories of my childhood."
It isn't enough, he said, "to protect wilderness just for people who can afford to go to it. I think bringing kids out to the wild is unquestionably the right thing to do. These kids have pretty tough lives. It opens their eyes to the world outside of their neighborhood. Some of the kids will grow up to protect the land they learn to love. You could look at it as an investment into the environment."
When making donations, Gelbaum usually insists that his identity not be revealed -- out of concern, he says, for his family's security.
Besides, he said, "I don't think that if you have a lot money and you give away a lot of money, you should get a lot of recognition. You shouldn't be able to buy that."