Ashton Kutcher looks like he might punch someone in the face.

He is standing on stage in a basement conference room at a midtown-Manhattan hotel, in front of a wall of flashing cameras, flanked by his wife, Demi Moore, and assorted do-gooders. Kutcher and Moore are here, at the Clinton Global Initiative—an annual conference hosted by the former president that addresses issues like HIV and debt relief—to talk up their own philanthropic efforts. The year-old Demi & Ashton (DNA) Foundation is launching its first project, Real Men Don't Buy Girls, an advocacy campaign to fight child-sex-slave trafficking in the United States.

Kutcher is getting emotional. He's talking about pimps raping 13-year-old girls. "It's an uncomfortable issue," he says, his voice laced with anger and frustration. "Trust me. When we're sitting down with our girls at the dinner table talking about human trafficking, it's awkward. But our children need to know about it."

When he's finished, Moore puts a comforting hand on his back and mouths, "Good job." But it's another hand that guides Kutcher to his next appearance—that of Trevor Neilson, the man directing this show. A Hollywood philanthropy consultant, he pairs celebrities with causes and helps them transform from the world's biggest stars into its most responsible citizens, one photo op at a time.

Neilson, a 38-year-old with dark good looks and exceptional credentials—Clinton White House intern, director of public affairs and director of special projects at the Gates Foundation, Council of Foreign Relations member—is the co-founder and president of Global Philanthropy Group (GPG). When celebrities want to rebuild Haiti, fight breast cancer, or maybe just burnish a tarnished public image by doing something, he is the man they call. He has worked with Angelina and Brad, Bono, both Bills (Clinton and Gates), Rihanna, Ben Stiller, Jim Carrey, Shakira, and Avril Lavigne, just to name a few. For fees upward of $170,000 a year, he matches an A-list client to a cause, sets up a strategy and a foundation, secures meetings on Capitol Hill, brings other wealthy backers on board, and summons the media to cover every saving-the-world moment along the way. In 2006, Neilson was the PR point man in the fierce bidding war for the first exclusive photos of Angelina Jolie's adopted Cambodian son, Maddox. As part of the deal he brokered, People magazine was obligated to report on the needs of the Cambodian people in exchange for the pictures.

"Artists are brands," says Neilson, standing in the hotel lobby at the Clinton Global Initiative, hobnobbing with every third person who walks past. "I see a need and a business opportunity to build those brands." Neilson is impressively smart, earnest in the manner of a D.C. policy wonk, and, as is clear in the bustling who's-who environment of the conference, tremendously well-connected. "You should know this guy," he says, interrupting himself to grab the attention of the head of Brad Pitt's home-rebuilding charity in New Orleans. The man says he needs $5 million. "Walk upstairs, it's early in the day," Neilson says with a laugh. The chief of Richard Branson's charitable foundation passes by. "You left Necker Island for this?" Neilson asks her, referring to the tycoon's private Caribbean getaway. YouTube's Chad Hurley walks over and Neilson invites him to the Shakira concert that night at Madison Square Garden. Hurley can't; his wife made other plans. "Jim Carrey will be with us," says Neilson. "It will be a blast, man."

"This guy is plugged in on so many levels—politics, charity, the media," says Andrew F. Cooper, a distinguished fellow at the Centre for International Governance Innovation in Ontario and the author of Celebrity Diplomacy. "He's working in a remarkable new niche market."

But Neilson sees himself as both a trailblazer and a chip off the old block. His father was an Olympia, Washington, family-court judge, and his mother ran an international child-welfare and adoption service; both practiced the liberal values they preached. They discovered children in need and adopted them—four to be exact, Neilson's two African-American brothers and his two Korean sisters. In other words, doing good was part of his upbringing.

•••

Neilson and his wife, Maggie, run GPG out of small offices in Santa Monica, California, two blocks from the beach. The pair oversee 15 staffers—mostly energetic twentysomethings fresh from M.B.A. and public-policy programs—and work with roughly 20 clients at a time. The atmosphere is more collegiate think tank than Hollywood glam.