Olga Aleksandrovna Ladyzhenskaya (Russian: Óльга Алекса́ндровна Лады́женская, IPA: [ˈolʲɡə ɐlʲɪˈksandrəvnə ɫɐˈdɨʐɨnskəɪ̯ə] (About this soundlisten)) (7 March 1922 – 12 January 2004) was a Soviet and Russian mathematician. She was known for her work on partial differential equations (especially Hilbert's 19th problem) and fluid dynamics. She provided the first rigorous proofs of the convergence of a finite difference method for the Navier–Stokes equations. She was a student of Ivan Petrovsky. She was awarded the Lomonosov Gold Medal in 2002.
Ladyzhenskaya was born and grew up in Kologriv. She was the daughter of a mathematics teacher who is credited with her early inspiration and love of mathematics. In October 1937 her father was arrested by the NKVD and soon killed. Young Olga was able to finish high school but, because her father was an "enemy of the people", she was forbidden to enter the Leningrad University. After Joseph Stalin's death in 1953, Ladyzhenskaya presented her doctoral thesis and was given the degree she had long before earned. She went on to teach at the university in Leningrad and at the Steklov Institute, staying in Russia even after the collapse of the Soviet Union and the rapid salary deflation for professors. Ladyzhenskaya was on the shortlist for potential recipients for the 1958 Fields Medal, ultimately awarded to Klaus Roth and René Thom.