Johnson Thomas Umunnakwe Aguiyi-Ironsi (3 March 1924 – 29 July 1966) was a senior Nigerian military officer and the first Nigerian Military Head of State. He seized power in the ensuing chaos following the 15 January 1966 military coup, serving as the Nigerian Head of State from 16 January 1966 until his murder on 29 July 1966 by a group of mutinous Northern army soldiers who revolted against his government in what was popularly called the July Counter Coup.
Thomas Umunnakwe Aguiyi-Ironsi was born to his father Mazi (means Mister in Igbo) Ezeugo Aguiyi on 3 March 1924, in Umuahia-Ibeku, present-day Abia State, Nigeria. He was eight years old, when he moved in with his older sister Anyamma, who was married to Theophilius Johnson, a Sierra Leonean diplomat in Umuahia. Aguiyi-Ironsi subsequently took the last name of his brother-in-law as his first name, who became his father figure. At the age of 18, Aguiyi-Ironsi joined the Nigerian Army against the wishes of his sister.
Aguiyi-Ironsi had his primary and secondary school educations in Umauhia and in Kano.
In 1942, Aguiyi-Ironsi joined the Nigerian Army, at the rank of a private with the seventh battalion. He got promoted in 1946 to the rank of company sergeant major. Also in 1946, Aguiyi-Ironsi was sent on an officer training course in Staff College, Camberley, England. In 1949, after completion of his course at Camberley, he was promoted second lieutenant of Royal West African Frontier Force.
Aguiyi-Ironsi was promoted to captain in 1953 and again promoted to Major in 1955. He was part of the officers who served as Queen Elizabeth II of the United Kingdom and Nigeria’s equerry at the time she visited Nigeria in 1956.
In 1960, Aguiyi-Ironsi was made commandant of the fifth battalion in Kano, Nigeria, with the rank of lieutenant colonel
Later in 1960, he headed the Nigerian contingent force of the United Nations Operation in the Congo. From 1961-1962, Aguiyi-Ironsi served as the military attaché to the Nigeria High Commission in London United Kingdom. During this period he was promoted to the rank of brigadier general and during his tenure as military attaché he attended some courses at the Imperial Defence college (renamed Royal College of Defence Studies in 1970), Seaford House, Belgrave Square.
In 1964 he was appointed at the commandant of the entire United Nations peace keeping forces in the Congo.
In 1965, Aguiyi-Ironsi was promoted to the rank of major general. that same year major general CB Welby-Everard handed over his position as the general officer Commanding, GOC of the entire Nigerian Army to Major General Johnson Thomas Umunnakwe Aguiyi-Ironsi (making him the first Nigeria indigenous to head the entire Nigerian Army).
In January 1966, a group of army officers, led by Major Chukwuma Nzeogwu, overthrew the central and regional governments of Nigeria, killed the prime minister, and tried to take control of the government in a failed coup d'état. Nzeogwu was countered, captured and imprisoned by major general Johnson Aguiyi-Ironsi.
Aguiyi-Ironsi was named military head of state on 17 January 1966, a position he held until 29 July 1966, when a group of northern army officers revolted against the government, and killed Aguiyi-Ironsi.