Fritz Zwicky (February 14 1898 – February 8 1974) was a Swiss astronomer, born in Varna, Bulgaria to Swiss parents.

In 1925 he came to the California Institute of Technology in the United States and remained there for the rest of his life, though he remained a Swiss citizen. He is famous for having called his colleagues "spherical bastards" because they were bastards no matter which direction one watches them from.

He was the first to use the virial theorem to deduce the existence of dark matter. He proposed the use of gravitational lenses. With Walter Baade, he came up with the idea that supernovae could create neutron stars and produce cosmic rays.

He also pioneered and promoted the use of Schmidt telescopes.

In his later career, he compiled a Catalogue of Galaxies and of Clusters of Galaxies (CGCG).

He won the Gold Medal of the Royal Astronomical Society in 1972.

The asteroid 1803 Zwicky was named in his honour.

de:Fritz Zwicky fr:Fritz Zwicky sl:Fritz Zwicky