Freidlin and Wentzell are the authors of the first monograph on the large deviations theory for stochastic processes (1979).
[1] He began studying mathematics at Moscow State University at the age of 16,[1] and earned a candidate's degree there in 1962, under the supervision of Eugene Dynkin.
However, growing anti-semitism in the Soviet Union prevented Friedlin from traveling and forced him to transfer from the Mechanics and Mathematics Department at Moscow State to the Bio-Physics Department (with the assistance of Andrey Kolmogorov in finding him this position).
By 1979 he had decided to emigrate to the US, but was denied permission to leave Russia; despite having no permanent employment for the next eight years, he continued to work and publish in mathematics.
[1] In May 2003, a conference on "Asymptotic Problems in Stochastic Processes and PDE's" was held at the University of Maryland in honor of Freidlin's 65th birthday.