Ask Bernard "Bernie" Marcus, co-founder of The Home Depot, why he decided to engage in philanthropy and he will say he never decided. "I just did it—you slide into it. I didn’t sit down one night with my wife, Billi, and say, ‘Maybe we'll become philanthropists.'"

Marcus's slide into philanthropy began while he was still building The Home Depot into the world's largest home-improvement retailer. When a young employee shared that he was dying of cancer, Marcus connected him to City of Hope, a cancer treatment center that ultimately saved the employee's life. "That impact was so important in my life," says Marcus. "I went to [City of Hope] and said ‘I want to join your board.' I had never done anything with philanthropy before…and I didn't have any money, but I worked diligently on that board."

Marcus's early habit of helping to meet the needs of the people around him by giving his time and managerial talent has become a strong theme in his philanthropy. Similarly, but with global consequences, Marcus observed the anguish of another employee, a young mother of an autistic child. To learn more about the disability, he toured the country's top medical centers and met countless families undergoing the same hardship. "Honestly, I didn't sleep for nights," says Marcus. "And I said, ‘Goddamn it, I'm going to do something about this.' And that's how we came about starting the Marcus Autism Center (MAC)—because of a need that I saw." Starting with two trailers in Atlanta, Marcus began to gather the best minds in medicine and other philanthropists to understand and treat the disorder.

In addition to supporting the people in his life, Marcus has also worked to give back to his local community. "We came to Atlanta broke—broke! If the Home Depot didn't make it, I was going to go into bankruptcy. We decided that we wanted to do something for the State of Georgia. We remembered the people that came and saved our lives," shares Marcus. A centerpiece of Bernie and Billi Marcus' efforts to give back to the community is the Georgia Aquarium in Atlanta, which has drawn billions of additional investment to help revitalize a blighted area of the city.

But throughout his philanthropy, whether he is supporting the people and places around him or his religious and cultural communities, Marcus's motivation remains the same: "It's really to save people's lives," he says. "That's the payoff. It's an emotional payoff that I can't explain to people."