Robert Louis Griess, Jr. (born 1945, Savannah, Georgia) is a mathematician working on finite simple groups and vertex algebras. He is currently the John Griggs Thompson Distinguished University Professor of mathematics at University of Michigan.
He received the AMS Leroy P. Steele Prize for a Seminal Contribution to Research in 2010.
Griess is a member of the National Academy of Sciences (2020) and the American Academy of Arts and Sciences (2007). In 2012 he became a fellow of the American Mathematical Society. He was an invited speaker at the International Congress of Mathematicians in Warsaw in 1983.