(CNN)History reserves special ignominy for presidents denied a second White House term.
But as Jimmy Carter reflects on his life after learning he has cancer, the 39th U.S. President says he wouldn't swap the personal reward of his expansive post-presidency for four more years in office.
"My life since the White House has been personally more gratifying, although the presidency was obviously the pinnacle of political success," Carter, 90, said in a moving news conference in Atlanta on Thursday. "If I had to choose between four more years and the Carter Center, I think I would choose the Carter Center."
But he added: "It could have been both."
Carter admitted recently that he had no concrete plans when he left office stung by the Iran hostage crisis and a tepid economy.
"When we came home, I had no idea what I would do with the rest of my life. I was fifty-six years old, one of the younger survivors of the White House," Carter wrote in his latest book "A Full Life: Reflections at 90," which was published earlier this year.
Carter's first task back home in Georgia was writing an autobiography that charted the achievements and disappointments of an unfulfilled political career while he searched for a more permanent role.
Then, late one night, lying in bed after a few hours sleep, he had a revelation -- he would not just build a presidential library, but would set himself up as a freelance global mediator, statesman and global health advocate who would work across political and humanitarian divides.
"This was the birth of the Carter Center," the former president wrote.
The Carter Center's work would eventually recast the roles and expectations of ex-presidents, and his move into global relief and humanitarian work after the White House has been emulated by successors like Bill Clinton and George W. Bush.
Over the next three-and-a-half decades, Carter would venture into global hotspots, negotiate with rogue leaders like North Korea's dictators Kim Il Sung and Kim Jong Il and launch a broad, global humanitarian mission.
He fought to eradicate diseases afflicting hundreds of millions of people in tropical Africa, including river blindness, malaria, and trachoma. He plunged into civil wars and conflicts from Nepal to Ethiopia, the Balkans and Sudan and across the Middle East.
He is credited with helping to peacefully restore order in Haiti in 1994 after the overthrow of President Jean-Bertrand Aristide, averting the need for American military action at a moment when U.S. bombers were already in the air.
The Carter Center has monitored elections in 100 nations, and Carter and his beloved wife, Rosalynn, have also devoted a week of work every year to the charity Habitat for Humanity, which builds and renovates homes for poor families.
It was when he was on a trip to Guyana earlier this year, that he first became ill. Doctors back home diagnosed cancer on his liver, which has been removed, and then found the melanoma in his brain.
Carter said Thursday he still hopes that his medical condition and radiation treatment will allow him to travel to Nepal later this year for his annual mission -- his 33rd in a row -- for Habitat for Humanity.
Carter reflected Thursday that his role as president -- with responsibility for 350 million Americans -- and his humanitarian work called for different skills. But he said his time in the White House gave him the contacts and prestige necessary to carry out his Nobel-prize winning post-presidential vocation.
"We deal with individual people in the smallest and most obscure and suffering villages in the desert and in the jungles of Africa, and we've had programs in 80 different countries on the Earth for the poorest and most destitute people in the world," he said. "And that has been, I'd say, far more gratifying personally because we actually interact with families and with people."