Fritz Zwicky, Swiss-American physicist and astronomer (d. 1974)
Fritz Zwicky (; German: [ˈtsvɪki]; February 14, 1898 – February 8, 1974) was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical and observational astronomy. In 1933, Zwicky was the first to use the virial theorem to infer the existence of unseen dark matter, describing it as "dunkel Materie".