Roger Charles Louis Guillemin (born January 11, 1924) is a French-American biologist and neurologist. He received the National Medal of Science in 1976, and the Nobel prize for medicine in 1977 for his work on neurohormones. Guillemin and Andrew V. Schally discovered the structures of TRH and GnRH in separate laboratories. He helped in creating the Salk Institute in La Jolla, California where he worked until retirement in 1989.