MR THAE YONG HO, 55
Mr Thae was deputy ambassador at the North Korean embassy in London when he defected last August, making him the highest-ranking diplomat from Pyongyang to do so. He cited disillusionment with the Kim regime and worries about his children's future as the key reasons for his defection. Now an analyst at the Institute for National Security Strategy run by South Korea's intelligence agency, Mr Thae famously declared that "Kim Jong Un's days are numbered". Some experts said he could be the next target for assassination.
MR PARK SANG HAK, 49
Mr Park is known as North Korea's "Enemy Zero", the top target on the Pyongyang regime's hit list. His "crime"? Mr Park, a member of North Korea's elite who worked at the nation's propaganda office until his defection in 1999, has sent over two million balloons containing pro-democracy materials across the inter-Korea border in the hope of effecting change in the country. He claims to regularly receive threats via phone and e-mail. In 2011, police foiled an attempt by a North Korean former commando, armed with poison needles, to assassinate him.
DR AHN CHAN IL, 63
The political scientist is known in South Korea as the first North Korean defector to earn a doctorate after his defection in 1979. A soldier then, he had lost faith in the Pyongyang regime and crossed the demilitarised zone. Dr Ahn, who regularly speaks out against North Korea, has said he is ranked fifth on North Korea's assassination list.
MR KIM SUNG MIN, 55
Mr Kim runs the Seoul-based anti-Pyongyang radio broadcast Free North Korea Radio. The former North Korean propaganda officer was sentenced to death and fled in 1997, escaping via China and turning up in South Korea two years later.
MR LEE HAN YONG, 37
The nephew of late North Korean leader Kim Jong Il's consort Song Hye Rim, defected to South Korea via Switzerland in 1982. He changed his name and underwent plastic surgery to live a quiet life, but brought attention to himself by releasing a memoir in 1996. He was killed a year later after North Korean agents shot him in front of his apartment outside Seoul.
Chang May Choon