Johnson Thomas Umunnakwe Aguiyi-Ironsi (3 March 1924 – 29 July 1966) was a Nigerian military officer who served as the first military dictator and head of state of Nigeria. He seized power during the ensuing chaos after the 15 January 1966 military coup. Ironsi ruled from 16 January, until his assassination on 29 July 1966 during the July counter-coup. He was assassinated by a group of military officers from the Northern Region led by Murtala Mohammed.