Johnson Thomas Umunnakwe Aguiyi-Ironsi was a Nigerian military officer who was the first military head of state of Nigeria. He seized power during the ensuing chaos after the 15 January 1966 military coup.

The military dictatorship in Nigeria was a period when members of the Nigerian Armed Forces held power in Nigeria from 1966 to 1999 with an interregnum from 1979 to 1983. The military was able to rise to power often with the tacit support of the elite through coup d'états. Since the country became a republic in 1963, there has been a series of military coups in Nigeria.