Beauregard Stubblefield was an African American mathematician who, despite his excellent undergraduate record, was turned down for graduate work at several universities. He showed great determination and eventually was awarded a Ph.D. from the University of Michigan. He served at several universities including Oakland University in Michigan, the Appalachian State University in Boone, North Carolina and then at the U.S. Department of Commerce in Boulder, Colorado.
Find out more at: https://mathshistory.st-andrews.ac.uk/Biographies/Stubblefield/