Czeslaw Ryll-Nardzewski, born on October 7, 1926 and died September 18, 2015, he was a Polish mathematician.

Born in Wilno, Commonwealth of Poland, he was a student of Hugo Steinhaus.

At the age of 26 he became professor at the Warsaw University.

In 1959, he became a professor at the Wroclaw University of Technology.

His main research areas are measure theory, functional analysis, foundations of mathematics and probability theory.

Several theorems bear his name: the Ryll-Nardzewski fixed point theorem, the Ryll-Nardzewski theorem in model theory, and the Kuratowski–Ryll-Nardzewski measurable selection theorem.

He became a member of the Polish Academy of Sciences in 1967.

Czesław Ryll-Nardzewski died in 2015 at the age of 88.