Jimmy Carter strides through an impoverished neighborhood of the Dominican town of Dajabon, where cattle mope behind a tangle of barbed wires, 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 sun-drenched 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 like 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, an 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 life could end next week or next decade.

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 Carter 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 Carter's 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, shows that smile once again, grinning ear to ear.

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

MODEST UPBRINGING

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," Young says.

There's one lonely balcony in Carter's hometown of Plains, a southwest Georgia town that is exactly how it sounds: Flat as a dime. Carter's up there sitting in his rocking chair, waiting for the start of a parade that celebrates his town's two biggest exports — peanuts and a president.

Carter still makes his home here and has deeded the family farm to his children and grandchildren in hopes that the latest generation of Carters can explore the same woods that he did as a child. He still drops by City Hall, pokes his head into the local bed and breakfast, strolls along the quiet downtown streets where he once sold boiled peanuts.

The town's population of about 500 has stayed about the same since Carter was a little boy. Nowadays, they call this part of Georgia "Presidential Pathways" and tourists wander around his old high school, explore his modest campaign headquarters, visit the church up the road.

The giant wooden cross hanging on the chapel of the Maranatha Baptist Church was built by Carter at the woodshop in his house. So were the wooden collection bowls that ushers passed around during breaks.

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

He sprinkles his lessons with personal stories, like the one where he tried fasting with a group of rabbis, and the one where he jogged around the ancient wall that circles the Old City of Jerusalem before sunrise.

"That's a bragging session," he says, with a laugh.

DRIVEN BY FAITH

His faith in Christianity has forged a "perpetual ministry," as the Rev. Joseph Lowery calls it, a nagging urge to do more. Carter says it's a "constant pressure from my deep religious faith to reach for improvement at all times, to recognize my own fallibilities and my own mistakes."

"He believes it's important to try to help people. It's unbelievable how he mobilizes his energy, the way he speaks so openly and so forcefully," said Fernando Henrique Cardoso, Brazil's former president and a longtime friend of Carter's. "And he's happiest when he's achieving."

But his faith also gives him a reservoir of happiness in an unstable world, he says, something to fall back on when he feels overwhelmed.

His Sunday school lesson on this sunny morning speaks to that. It 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."