Lothar Collatz
Collatz studied at universities in Germany, including the University of Berlin under Alfred Klose. He received his doctorate in 1935 for writing a paper about linear differential equations. He worked as an assistant for the university. Then, he worked at the Technical University of Karlsruhe in 1935. He habilitated (achieved the highest university degree in European countries) in 1937. He worked as a Privatdozent (sign of position given to special students in Europe) from 1938 to 1943. He worked with Alwin Walther at the Institute for Practical Mathematics. Collatz worked at the University of Hamburg from 1952 until 1978. There, he created the Institute of Applied Mathematics. After leaving his job, he continued to be active.