From Prison to the President’s Office: A Former Radical Helps Shape Korean Detente

Moon’s chief of staff, who in years past voiced skepticism about U.S. role, leads outreach to Pyongyang

A meeting between President Donald Trump and North Korean dictator Kim Jong Un could be a diplomatic breakthrough, but both men are nothing if not unpredictable.
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SEOUL—In 1989, South Korean authorities charged a young political activist named Im Jong-seok with colluding with the enemy after he helped a fellow student make a secret, illegal trip to North Korea to meet the country’s then-dictator Kim Il Sung—a propaganda coup at the time for Pyongyang.

Nearly three decades later, Mr. Im, now chief of staff to South Korea’s president, is playing a leading role in Seoul’s diplomatic outreach to Pyongyang, helping set the stage for meetings between the two Koreas’ leaders Friday and between...