Robert G. Greenler is an American Physicist. His research centered on the optical properties of surfaces. Greenler received his B.S. from the University of Rochester and a Ph.D. from Johns Hopkins University. He taught Physics at the University of Wisconsin–Milwaukee from 1962-1992. He became Professor Emeritus of the same university after his retirement. Professor Greenler was president of the Optical Society of America in 1987. He was the recipient of the Robert A. Millikan award in 1988.