Jeong Nam-gyu was born on April 17, 1969, in Jangsu County, South Korea.

On January 14, 2004, in Bucheon, Gyeonggi Province, Jeong Nam-gyu kidnapped, raped, and murdered two children, Yoon Ki-hyun, aged 13, and Im Young-gyu, aged 12. After this, he continued to kill people in Gyeonggi and Seoul. His victims included a woman who was returning home late at night. Jeong committed many of his murders in southern parts of Seoul, specifically in areas like Shin-gil, Guro, and Gwanak. His actions also included the murder of a male elementary school student, which he claimed was influenced by his own childhood abuse.

On January 30, 2004, Jeong stabbed Won Kyung-ja, who survived the attack. He continued his violent acts by stabbing Jeon Hyo-sil on February 6 and Son Young-ran on February 10, both of whom died. He attacked several more individuals in the following weeks, resulting in more deaths and injuries.

On April 8 and April 22, 2004, Jeong murdered Jeong Yong-soo and Kim Young-hee, respectively. He also attacked others who survived, including Choi Joo-myung on May 5. His violence continued with the murder of Kim Hyun-jin on May 9. In August 2004, he bludgeoned Ahn Sung-chul, who survived the assault.

In 2005, his crimes escalated further. He attacked a 71-year-old woman and a 13-year-old girl in April, then set their residence on fire. In May, he killed Kim Young-soon and attacked more victims that year.

On January 14, 2006, he assaulted a 7-year-old girl but fled when her father intervened. Later that month, he murdered Song Jin-hee and her siblings in a brutal attack.

His final attacks occurred in March and April 2006, resulting in several victims, with only one surviving.

On April 26, 2006, Jeong was arrested after a fight when he attempted to kill two people. He later confessed to the murder of a man in Imun-dong, which had previously been falsely confessed by another serial killer, Yoo Young-Chul. On April 12, 2007, Jeong was sentenced to death by the Supreme Court.

On the morning of November 21, 2009, while in prison, Jeong attempted to hang himself using a plastic bag. He was taken to the hospital but died the following day.