He also served as vice-chairman of the National Defence Commission of North Korea, head of the Operations Department from April 2009 to June 2016.

[2][3] Together with So Sang Guk and Jon Pyong Ho, O led the early stages of the North Korean nuclear weapons programme.

Nevertheless, he was considered among "senior officials of party, state, army, security organs, and national institutions".

[6] In June 2009, O was identified by international authorities and the United States government as a key figure in North Korea's currency counterfeiting activities, specifically with United States one hundred-dollar bills, known as Superdollars.

[8][9] O Kuk-ryol took part at a meeting of top leaders held immediately after Kim Jong Il's death on 17 December 2011 to plan the funeral and succession.

[11] After the execution of Jang Sung-taek in December 2013, a powerful rival, O re-emerged as more of a public figure.