Paul Turán's Ph.D. was supervised by Féjér, but, being Jewish, he could not obtain a job (even as a school teacher). He spent 32 months in a Nazi labour camp from 1941 to 1944 in Hungary. From 1949 he was professor at Budapest University.
Turán's first work was on probabilistic number theory and in 1938 he produced the sum-power method on which he wrote 50 papers during his life. He also worked on extremal graph theory (while in the labour camp) and statistical group theory with Erdös. The reference below, written by Paul Erdös, describes Turán's work on graph theory.
A mathematician who served under Turán in Budapest described him as
outstanding in analytic number
theory.