Harvey James Alter is an American medical researcher, virologist, physician and Nobel Prize laureate, who is best known for his work that led to the discovery of the hepatitis C virus. Alter is the former chief of the infectious disease section and the associate director for research of the Department of Transfusion Medicine at the Warren Grant Magnuson Clinical Center in the National Institutes of Health (NIH) in Bethesda, Maryland. In the mid-1970s, Alter and his research team demonstrated that most post-transfusion hepatitis cases were not due to hepatitis A or hepatitis B viruses. Working independently, Alter and Edward Tabor, a scientist at the U.S. Food and Drug Administration, proved through transmission studies in chimpanzees that a new form of hepatitis, initially called "non-A, non-B hepatitis" caused the infections, and that the causative agent was probably a virus. This work eventually led to the discovery of the hepatitis C virus in 1988, for which he shared the Nobel Prize in Physiology or Medicine in 2020 along with Michael Houghton and Charles M. Rice.