Paul Ehrenfest (January 18, 1880 – September 25, 1933) was an Austrian physicist and mathematician from Vienna. He died in 1933 in Leiden, the Netherlands. His major contributions include the theory of phase transition.
He married the Russian mathematician Tatyana Alexeyevna Afanasyeva (1876–1964), who collaborated with him in his work.
He suffered from low self-esteem and constant doubts about his abilities, and died by suicide.