At a dinner hosted by North Korean leader Kim Jong Un for a delegation from the South this week, a bespectacled official leaned forward to talk to a grinning Mr. Kim—a scene captured in a photograph displayed prominently in the North’s largest newspaper.
The 63-year-old career intelligence officer was instrumental in back-channel contacts that led to the two inter-Korean summits in 2000 and 2007. In both those cases, Mr. Suh met extensively with Mr. Kim’s father, North Korea’s then-leader Kim Jong Il.
Mr. Suh—who is set to travel to Washington to brief U.S. officials on his visit to the North and
Mr. Kim’s assertions that he is open to disarmament talks—has supported engagement with Pyongyang, while at the same time expressing deep doubts about the North’s trustworthiness and intentions. 
He is also a vocal supporter of Seoul’s alliance with Washington, and told South Korean lawmakers last year that the country should flatly reject any calls by North Korea to remove U.S. troops from the Korean Peninsula—even if North Korea promises to dismantle its nuclear programs. In July 1997, he became the first South Korean official to be sent to live in the North, as part of efforts to construct light-water reactors in the North following a 1994 deal between Pyongyang and Washington to freeze North Korea’s nuclear program.
He gained more experience in following years, working to arrange summit meetings between the two sides—a process that involved spending time with North Korea’s previous leader, Kim Jong Il, the father of Kim Jong Un.
“Kim Jong Il was fond of Suh,” said Chung Dong-young, a former unification minister and current lawmaker who traveled to the North with Mr. Suh in 2005. In that meeting, aimed at persuading North Korea to return to denuclearization talks, Mr. Chung said he, Mr. Suh, and Kim Jong Il spent five hours together.
In 2008, Mr. Suh wrote a doctoral dissertation on the aims of North Korea’s nuclear-weapons programs, arguing that they were aimed ultimately at letting Pyongyang strike some kind of security deal with Washington.
“The North’s pursuit of nuclear weapons cannot persist as an eternal strategy,” Mr. Suh wrote in his dissertation, which was later published as a book. “Eventually, such a foreign policy will become an institutional constraint limiting North Korea’s growth.”