William C. Campbell, Irish-American biologist and parasitologist, Nobel Prize laureate

William Cecil Campbell is an Irish-American microbiologist known for his work in discovering a novel therapy against infections caused by roundworms, for which he was jointly awarded the 2015 Nobel Prize in Physiology or Medicine. He helped to discover a class of drugs called avermectins, whose derivatives have been shown to have "extraordinary efficacy" in treating River blindness and Lymphatic filariasis, among other parasitic diseases affecting animals and humans. Campbell worked at the Merck Institute for Therapeutic Research 1957–1990, and has become a research fellow emeritus at Drew University.

The Nobel Prize in Physiology or Medicine is awarded yearly by the Nobel Assembly at the Karolinska Institute for outstanding discoveries in physiology or medicine. The Nobel Prize is not a single prize, but five separate prizes that, according to Alfred Nobel's 1895 will, are awarded "to those who, during the preceding year, have conferred the greatest benefit to humankind". Nobel Prizes are awarded in the fields of Physics, Medicine or Physiology, Chemistry, Literature, and Peace.