Robert Joseph Lefkowitz (born April 15, 1943) is an American physician (internist and cardiologist) and biochemist. He is best known for his work with G protein-coupled receptors, for which he was awarded the 2012 Nobel Prize for Chemistry with Brian Kobilka. He is currently an Investigator with the Howard Hughes Medical Institute as well as a James B. Duke Professor of Medicine and Professor of Biochemistry and Chemistry at Duke University.