Michael Ernest O'Nan (August 9, 1943, Fort Knox, Kentucky – July 31, 2017, Princeton, New Jersey)[1] was an American mathematician, specializing in group theory.
[2] O'Nan received his PhD in 1970 from Princeton University under Daniel Gorenstein with thesis A Characterization of the Three-Dimensional Projective Unitary Group over a Finite Field.
In 1976 he found strong evidence for the existence of a sporadic group,[4] which Charles Sims constructed.
[5] The O'Nan–Scott theorem in group theory is also named after O'Nan, who discovered it independently from Leonard Scott.
It describes the maximal subgroups of the symmetric groups.