Ilya Ilyich Mechnikov (15 May [O.S. 3 May] 1845 – 15 July 1916), gallicised and known in Western sources as Élie Metchnikoff, was a zoologist from the Russian Empire of Moldavian noble ancestry best known for his research in immunology (study of immune systems) and thanatology (study of death). He and Paul Ehrlich were jointly awarded the 1908 Nobel Prize in Physiology or Medicine "in recognition of their work on immunity".
Mechnikov was born in a region of the Russian Empire that is today part of modern-day Ukraine to a Moldavian noble father and a Ukrainian-Jewish mother. He later moved to France. Given this complex heritage, five different nations and peoples lay claim to Metchnikoff. Despite having a mother of Jewish origin, he was baptized Russian Orthodox, although he later became an atheist.