Gary Michael Seitz (May 10, 1943 – October 30, 2023) was an American mathematician, a Fellow of the American Mathematical Society[1] and a College of Arts and Sciences Distinguished Professor Emeritus in Mathematics at the University of Oregon.

Such information is important in its own right, but was also critical in the classification of the finite simple groups, a major achievement of 20th century mathematics.

Seitz made contributions to the classification of finite simple groups, such as those containing standard subgroups of Lie type.

He served as thesis advisor for ten PhD students of whom eight currently hold academic positions.

In 2004, about a dozen mathematicians gathered for an international conference at the University of Oregon to honor his work.