Hwang Jang-yeop (황장엽) recently died, I read in the news. This man was the highest ranking member of the North Korean government ever to have defected, having done so in 1997. He was notable as having been both Kim Il-sung's and later Kim Jeong-il's "ideology advisor." In the 1970's, he was chairman of the North Korean parliament.
In fact, he was basically the key author of the Juche concept, which is North Korea's official state ideology (in opposition to Marxist-Leninism, Stalinism, or Communism, which are inaccurate terms often applied to the regime in the West). Hwang Jang-yeop defected not because he'd become disillusioned with the Juche concept that he'd authored, but rather because he felt the North Korean regime was only paying lip service to it, and that the Kims (father and son) were in essence guilty of having implemented feudalism rather than any type of communism, Juche or otherwise.
He was originally embraced by the South Koreans when he came over, but during the presidencies of Kim Dae-jung and Roh Mu-hyeon, with their "sunshine policy" toward the North, he was marginalized, as those governments made efforts to avoid antagonizing Kim Jeong-il.