At the age of 25, wrote his now celebrated paper, Acta Mathematica. Emigrated after the October Revolution 1917. His first work, on the Galois theory of algebraic equations, was published when he was 19 years old.
Taught at Hamburg University. Professor at Basel, 1923. Taught there until his retirement in 1961.
His 3 textbooks, written in 1940, are still widely used to train mathematicians and other scientists.