I believe it should be General Murtala Muhammed. He was appointed the Head of State on the 30th of July, 1975 and then assasinated on Feb 13th, 1976 at the age of 37 (Less than 7 months).
During his short period as the Head of state, He:
1) Scrapped the 1973 census, which was weighted in favor of the north, and to revert to the 1963 count for official purposes.
2) More than 10,000 public officials and employees were dismissed without benefits, on account of age, health, incompetence, or malpractice.
3) He removed top federal and state officials to break links with the Gowon regime and to restore public confidence in the federal government.
4) He also announced that his government would encourage the rapid expansion of the private sector into areas dominated by public corporations. He reappraised foreign policy, stressing a "Nigeria first" orientation in line with OPEC price guidelines that was to the disadvantage of other African countries.