Lt Colonel Yakubu Gowon, the Chief of Army Staff under Ironsi, became the Head of State and Commander-in-Chief of the Armed Forces after the bloody coup d’etat of 29th July, 1966 which led to the assassination of General Aguiyi Ironsi and Lt. Colonel Adekunle Fajuyi, the military governor of Western Nigeria and several military officers mainly of Igbo extraction. Ironsi was killed while on a state visit to the Western Region.

The presidential system of government is based on separation of power where the Executive is separated from the Legislature. It can also be regarded as a system where executive powers are invested in one person called the president and in which the Executive arm of government is separated from the Legislature but equal to it.