Jimmy Carter strides through an impoverished neighborhood of the Dominican town of Dajabon, where cattle mope behind a tangle of barbed wire, where the heat suffocates and the air is thick with mosquitoes.

He marches to a bluff overlooking a river, the sun glinting off his "JC" belt buckle, followed by a pack of barefoot children and their parents. He clutches each hand that comes his way, occasionally dropping a "muchas gracias" laced with his Southern twang.

When he gets to a hovel owned by Juan Taveres, a weathered grandfather whose family was once afflicted by malaria, he eases into a rocking chair. Roosters crow, reporters shuffle, but it seems that they could talk all day, if not for the waiting convoy rumbling up the hill.

"There's no malaria here, right?" Carter asks.

No, Juan responds eagerly.

"And none in the future," Carter declares.

He flashes that smile - the megawatt grin beloved of editorial cartoonists, the incongruous trademark of a disappointing, one-term presidency.

Nearly three decades have passed since Carter left office. He is 85 years old. Yet here he is, in a torrid, desolate corner of the world, pushing two reluctant Caribbean neighbors to fight malaria, a disease that's long been eradicated from richer countries.

And he is smiling, because this is what he does. Since leaving the White House, he's logged millions of miles and visited dozens of countries on missions to wipe out diseases, mediate conflicts, advocate for human rights, and monitor elections. He's built a legacy that few, if any, American ex-presidents can match.

"I would say that this life, for the last 25 or 30 years since we left the White House, has been the most enjoyable and the most gratifying," he says.

He'll tell you his motivation stems from a frustrating desire to solve what he believes are solvable problems, from seemingly eternal international conflicts to public health dilemmas. He'll also admit it's driven by his growing sense of mortality, an understanding that his time grows short.

But the ex-president's age is also an ally. It gives him "great solace" as he contemplates the inevitable, he says, a feeling of equanimity that helps even out his competitive nature. It's all driving him to make the most of this phase of his life - even if the grueling pace reminds him of those tiring days of his childhood on the farm.

His wife, Rosalynn, has a simpler explanation.

With a shrug, she says: "He's miserable if he's not doing anything."

"I get this feeling he has this Schindler's List going on," says John Stremlau, a longtime friend who heads the Carter Center's peace programs. "He wants to squeeze every ounce of helping people that he can. It's inspiring and it's exhausting. I think he thinks every minute about what he can be doing."

Even some of Carter's closest friends say they were skeptical when he first outlined his post-presidential plans. Stuart Eizenstat, who was his domestic policy adviser, remembers that most of Carter's inner circle thought the president was being "overly dewy-eyed" when he dreamed up the idea of mediating those never-ending conflicts.

Almost three decades later, though, Atlanta's Carter Center is the embodiment of that legacy. And on the warm October day when he turned 85, it staged a reunion of sorts. His top political allies, four generations of his family, and hundreds of others convened to celebrate the center's newly renovated museum.

Carter, surveying the crowd from a stage, showed that smile once again, grinning ear to ear.

His supporters, all these years later, are still quick to rush to his defense.

Walter Mondale, his vice president, says that Carter took the political heat up front "so we could all be better off." Andrew Young, Carter's ambassador to the United Nations, says it might take a few more decades for historians to realize the impact of Carter's term in office.

"It took 100 years to understand Jefferson. It took 100 years for people outside the North to understand Lincoln. And it's got to take at least 50 years to understand Carter," says Young.

And Douglas Brinkley, a Rice University history professor who has written a book about Carter, says Carter's presidency may be more fondly remembered overseas than at home.

"Pick the country - they view him as one of the most successful presidents," said Brinkley. "He has helped America's image around the world because he's been able to make everyone trust him. And he earns that trust because he's honest."

Carter himself wants to be remembered at least as much for his work outside Washington as he does in it. The museum renovation speaks to that - it devotes more space than any other presidential library to time outside the White House.

"I'd like to be associated with the words peace and human rights," he says. "Peace, hope, human rights."

And so he continues to wander the globe at a pace that would exhaust men half his age.

His travels - such as his trip to the Balkans in 1994 to try to broker a cease-fire - often draw criticism. Few controversies have earned him more ire than his rebukes of Israel in his quest for Middle East peace, what he calls his greatest unfulfilled mission.

He pays no heed to the critics.

"It seems foolish for him to worry about what the secretary of state tells him over his conscience - he's going to listen to his conscience," says Brinkley, the historian.

Like his father before him, Carter teaches regular Sunday school classes at Maranatha Baptist Church in his hometown of Plains. It's a big to-do, with people gathering two hours before he begins, but nothing like it was in the 1980s when folks would line up at the church before dawn.

His Sunday school lesson on this sunny morning focuses on Nehemiah, who gave up a lucrative job after intense prayer and decided to move to Jerusalem and rebuild the city.

"We all have problems and we all have difficult decisions," Carter says. "And we should do exactly what Nehemiah does - pray and ask God for guidance."