SEOUL—As the U.S. and North Korea track an unsteady course toward a nonnuclear North, Seoul is trying to sustain the engagement by deploying a veteran adviser with the distinction of being respected in both Washington and Pyongyang.
Moon Chung-in, special adviser to South Korean President Moon Jae-in, said in an interview that U.S.-North Korea talks are stalled—and that Seoul aims to prod both sides to keep moving in the direction of disarmament and peace.
While “the U.S. is demanding North Korea front-load vows to declare and accept inspections of its nuclear arms” before easing sanctions, South Korea encourages mutual concessions that can build trust—and is trying to ease the process, he said. South Korea, for instance, has offered to host talks between U.S. and North Korean officials.
President Trump has repeated assurances that North Korean leader Kim Jong Un is committed to denuclearization, after the two met in Singapore in June. But some U.S. officials, such as national security adviser John Bolton, have expressed skepticism. North Korea has said it dismantled a nuclear testing site, but outside monitors accused Pyongyang of failing to halt development of nuclear weapons.
Meanwhile, Seoul is preparing for the third meeting this year between President Moon and Mr. Kim, to be held in Pyongyang in September.
The U.S. Embassy in Seoul declined to comment on progress of engagement with the North.
Mr. Moon, 67 years old, has built relationships in both countries over the years. In 2000, North Korea allowed him to appear alongside South Korea’s future unification minister Lee Jong-seok on a panel in a live television broadcast from Pyongyang. In talks with South Korea, Pyongyang’s delegates often single out Mr. Moon’s recent published articles for praise, Mr. Lee said.
He lived in the U.S. for nearly two decades, studying and later teaching at colleges from 1978 until returning to Seoul in 1994. His son is an American citizen.
“The South Korean president has relatively few North Korea experts who are fluent English speakers and who know Americans well,” said a former senior U.S. diplomat in Seoul.
“This social capital is immensely valuable to the Moon administration, because [Moon Chung-in] has friends and colleagues across the political spectra in almost every country that matters to the Korean issue,” said Peter Hayes, director of the Nautilus Institute for Security and Sustainability, a research center in Berkeley, Calif., who coedited a book with Mr. Moon.
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Mr. Moon has played a role in steering public debate, and potentially influencing policy makers, through public comments that have tended to foretell the Seoul government’s direction.
During a period of heightened tension with North Korea last year, he said Seoul should reconsider conducting U.S.-South Korean military exercises in return for a halt to Pyongyang’s missile tests. The comments enraged South Korean conservatives. The government in Seoul didn’t publicly support Mr. Moon’s comments at the time.
The U.S. has traditionally called its exercises with South Korea “defensive in nature,” although Mr. Trump in June said they were “provocative,” a term commonly used by North Korean state media to describe the exercises.
Months later, the proposition became policy when President Moon sought to delay and downsize the exercises. In June this year, President Trump said he was suspending joint exercises and wanted to bring U.S. forces home.
“I would definitely say he’s close” to the South Korean president, a person in Seoul’s diplomatic circles said of Mr. Moon. “It’s not always clear when he’s speaking on guidance from the Blue House or somebody else. But it’s pretty clear that he is relevant.”
In late April, days after the first inter-Korean summit, Mr. Moon traveled to New York and Washington to hear what key American foreign affairs specialists had to say about the event. He visited the Council on Foreign Relations in New York and the Atlantic Council in Washington. He also huddled with former Secretary of State Henry Kissinger.
Daniel Sneider, a Stanford University lecturer who has known Mr. Moon since the early 2000s, said the South Korean is a supreme networker who knows how to sell Seoul’s “progressive agenda in a way that is more palatable to Americans.”
“He is there as a publicist more than as a policy maker,” he said.
Mr. Moon has drawn criticism, however, for comments that appeared to rationalize North Korean aggression, such as when he said the former South Korean government provoked a North Korean artillery barrage in 2010 that destroyed homes and killed four South Koreans.
Mr. Moon is “typical of South Korean progressives who…systematically ignore the brutal nature of the regime to present it as a purely rational actor,” said Mr. Sneider.
In the interview, Mr. Moon stressed that he considered the attack unjustifiable, but defended his past comments.
Similarly, he has criticized the North’s weapons program but puts it in a broader context. “North Koreans believe that the nuclear weapon is the only way to protect themselves from an American nuclear threat,” he said.
Mr. Moon’s straightforward yet subtle character was evident in his youth. In high school, he was a judo and shot-put champion who didn’t tolerate bullies, but also had a softer side, said longtime friend Koh Choong-suk. “He ghostwrote love letters for friends, and knew how to say the right words to girls,” Mr. Koh said.
Other acquaintances of Mr. Moon, who is from the resort island of Jeju, describe him as approachable and gregarious.
“The rice wine and liquor in Jeju are wonderful,” said Mr. Hayes. “He and the other Korean hosts can drink most international guests under the table.”
Write to Andrew Jeong at andrew.jeong@wsj.com