Longtime fans of "ER" will know that Dr. Mark Greene, the beloved character played by Anthony Edwards, died in the prime of his life from cancer in 2002. And current fans will know that he reappeared last week, during a series of flashbacks to when he still lived.

Edwards didn't reprise his role because he's hurting for work. Far from it. The 46-year-old actor has had roles in six films since he left "ER," including The Forgotten, Northfork and Zodiac. He reprised it because he saw a way to help countless children in Kenya.

For the past three years, Edwards has worked with Shoe4Africa, a non-profit dedicated to empowering Africans, particularly women and children, by providing them with running shoes, educating them about AIDS, and in its largest project to-date, building a children's hospital in Eldoret, Kenya.

The hospital was suggested by the Kenyan government after violence ripped through that country last January, and Edwards, along with S4A's founder, Toby Tanser, promptly agreed to build one. "When your overall mission is to help and empower people, a hospital just makes sense," Edwards says. "It's an essential element of health."

The next step was a little more daunting: raise $15 million, a first for Shoe4Africa, which up to now has relied entirely on volunteer efforts and simple shoe donations.

So when Warner Bros. approached Edwards about playing Dr. Greene, Edwards said sure, but with one condition: the production studio would donate $125,000 to the hospital. The studio agreed. Steven Spielberg soon joined the cause, donating an additional $125,000, and the producer John Wells gave $50,000.

The donations gave the project some legs, and Edwards and Tanser are now taking an Obama-esque approach to fundraising. Using their networks of friends, colleagues, and philanthropists, and, of course, the Internet, the two friends have begun what may be the hardest marathon either has ever run. (Edwards ran the Chicago Marathon three times, and Tanser is a world-class athlete and one of the best runners to have ever come out of Iceland.)

The need is urgent and ongoing, says Edwards, who hopes the hospital will be built by 2010. When it opens its doors, the 250-bed Shoe4Africa Children's Hospital will be one of the largest in the world.

And when that happens, Shoe4Africa will walk away, allowing the hospital to function independently of the organization that built it. But that doesn't mean Shoe4Africa is walking away from the continent that gave it its name. Edwards says they plan to build a sports complex and a shoe factory, while increasing their outreach in Tanzania, Ethiopia, and Uganda, among other nations.

The shoe factory is key, says Edwards, because of the hookworm epidemic that has taken so many children's lives in Africa. "There are people in Africa who have tremendous spirit and enthusiasm," he adds, "but zero opportunity." Living in densely populated slums without water, clean food, or shoes, many Africans are forced to walk barefoot on disease-ridden roads. Once infected with hookworm, a person is much more susceptible to HIV, allowing the virus to spread even more rampantly than it does already. Giving a poor child or adult something as simple as a pair of shoes can make all the difference in the world.

"Shoes are like soap," Edwards says, "a basic element that we take for granted, but without which we get sick and die."

Edwards understands that his celebrity draws attention to the Shoe4Africa cause, and that's fine with him. "It's one thing to write a check to a charity, but it's much more fulfilling to get involved," he says. Having worked for years to raise awareness about autism, Edwards also recognizes that celebrities need to choose their causes carefully. "It's a thin veneer you're on already when you're a celebrity," he says, "and you can't spread it around too much. You have to pick one thing. And as long as [the charity] does what it says it's doing, it works."