Robert Griess is an American mathematician known for his contributions to group theory, particularly in the study of finite groups. He is recognized for his work on the classification of simple groups, which are the building blocks of all finite groups. Griess is also known for the construction of the first known example of a nontrivial simple group, called the Griess group. In addition to his research, Griess has held academic positions at various institutions, including University of Michigan and University of California, Santa Barbara. His work has had a significant impact on the field of mathematics, influencing both theoretical research and practical applications in algebra.