(FORTUNE Small Business) – The character of a person never changes as you go through life," says Millard Fuller, 70, founder of Habitat for Humanity. Now that he's no longer welcome at the charity's offices, we're meeting in the office Fuller uses in his home, on six acres of swampy woodland near Americus, Ga. He's leaning back in his chair. A plate of chocolate cookies is on the desk between us. "Your goals in life change," Fuller continues, warming to his homily. "In the Bible the apostle Saul was an aggressive persecutor of Christians. Then he was converted on the Damascus road, and he became an aggressive promoter of the Gospel. That's the same thing with me. I was an aggressive businessman. Then my goals changed, and I became an aggressive promoter of putting everybody in the world in a house."

This summer in Knoxville, Tenn., Habitat for Humanity will erect its 200,000th house (they're financed by donations, built with volunteer labor, and sold to low-income families at no profit with a zero-interest loan). That translates into shelter, maybe not for everybody in the world, but for one million poor people in 100 countries--an amazing legacy, though one threatened by scandal. In March 2004 a female Habitat employee accused Fuller of sexual harassment. Habitat hired a New York City law firm to investigate. The board says nothing was proven, and Fuller denies any wrongdoing. But in January the board, citing "public comments and communications ... that have been divisive and disruptive to the organization's work," fired Fuller and his wife, Linda, 64, who helped launch Habitat in 1976. Fuller is fighting back, raising money for Habitat projects and mustering support for reinstatement from old Habitat friends, among them former President Jimmy Carter. His firing, he insists, resulted from a classic clash between a charismatic founder intent on growth ("I want Habitat in every country on earth!") and his go-easy board.

Fuller developed an appreciation for growth by watching the struggles of his perfectionist father, a small-time grocer and frozen-custard-stand owner in Lanett, Ala. "If you're going to demand perfection, you're always going to run a real small operation," Fuller says. While in law school at the University of Alabama, Fuller went into business with classmate Morris Dees, whom he had met in the registration line. Their mission: "to get rich. Our idea was that if you have talent--if you can sing real good or shoot a basketball real good--you can make a lot of money, but if you don't have those talents you'd better learn how to sell." Fuller and Dees sold holly wreaths, birthday cakes, firecrackers, phone books, desk blotters, rat poison, tractor cushions, cookbooks, and whatever else they could buy cheap and unload quickly, and they did indeed get rich. "We bought big houses," says Fuller, "and 2,000 acres of land and horses and cattle and speedboats and brand new Lincoln Continentals to drive around and had maids and servants, and we weren't even 30 years old. It was a huge success."

The business was, that is. Fuller's personal life collapsed--a consequence, he says, of always working. Linda left him. Fuller pursued her from Montgomery to New York City. And there, in a taxicab on the way to the Wellington Hotel, Fuller says, he saw the light. Literally. "In that moment of light," he recalls, "this thought came into my head: Give all your money away." Fuller's priorities shifted dramatically. Dees's too: he founded the Southern Poverty Law Center. Yet how much, really, has either man changed? A social activist--that's someone who's not satisfied with the way things are, thinks about how they could be better, and follows through. Wait a minute: Isn't that an entrepreneur?