Mike was born in Fort Knox, Kentucky and was educated as an undergraduate at Stanford University and as a graduate student at Princeton University. While at Princeton he made contact with Danny Gorenstein, who became his thesis adviser.
His thesis (1969) reflected what would be a long-time interest: finite doubly-transitive permutation groups, explored with block designs and related combinatorial structures. The thesis was a characterization, among doubly transitive groups, of the three-dimensional unitary groups over finite fields. After a year or two at the University of Chicago, Mike came to Rutgers, shortly after Gorenstein did. He quickly reached the rank of full professor. Through the 1970's he was the leading figure in the world in the study of finite doubly transitive groups, bringing original and effective ideas to the effort to classify them. In a remarkable series of papers he completed the classification except for a single case--doubly transitive groups in which the stabilizer of a point is a simple group, or "almost" simple. Shortly after that the tidal wave of the classification of finite simple groups washed over the whole area and as a result, in my opinion, Mike's work has not received the long-term recognition that it deserves.
He will be remembered for his 1975 discovery of one of the sporadic finite simple groups, called the O'Nan group or the O'Nan-Sims simple group, since it was Charlie Sims, partly in collaboration with Sims's student Steve Andrilli, who proved the existence and uniqueness of the group, after Mike had predicted many properties of the group. Following the classification of simple groups, he independently proved what has come to be known as the O'Nan-Scott Theorem or Aschbacher-O'Nan-Scott Theorem. It is a taxonomy of maximal subgroups of the finite alternating and symmetric groups, and a related taxonomy of all finite primitive permutation groups. It has been widely used in finite group theory since 1980, being a tool that fits naturally with the classification of finite simple groups.
Mike was quick-witted, and widely admired and liked in the world of finite group theory. He was a generous teacher and a loyal friend. He had one Ph.D. student, Dick Stafford, of the National Security Agency. As one of his colleagues has written, his good cheer and twinkling smile radiated happiness at being in the game of life.