NIH Image Gallery from Bethesda, Maryland, USA · Public domain

Harvey Alter spent decades chasing a mystery hiding in blood transfusions: cases of hepatitis that matched neither the A nor B virus. His research team's work through the 1970s and 80s, including transmission studies establishing that a distinct, then-unidentified virus was responsible, laid the groundwork for the 1988 discovery of hepatitis C — a finding that transformed blood-supply safety worldwide. He shared the 2020 Nobel Prize in Physiology or Medicine with Michael Houghton and Charles Rice, and earlier received the Albert Lasker Award for Clinical Medical Research.