Lynn Margulis (born 1938) is a biologist and a professor at the University of Massachusetts Amherst. In 1967 she proposed a contentious new hypothesis which became her most important scientific contribution as the endosymbiotic theory of the origin of mitochondria as separate organisms that long ago entered a symbiotic relationship with eukaryotic cells through endosymbiosis.
She was criticized as a radical and her scientific work was rejected by mainstream biology for many years. Her work has more recently received widespread support and acclaim. Margulis was inducted into the World Academy of Art and Science, the Russian Academy of Natural Sciences, and the American Academy of Arts and Sciences between 1995 and 1998.