Max August Zorn (tsɔʁn; June 6, 1906 – March 9, 1993) was a German mathematician. He was an algebraist, group theorist, and numerical analyst. He is best known for Zorn's lemma, a method used in set theory that is applicable to a wide range of mathematical constructs such as vector spaces, and ordered sets amongst others. Zorn's lemma was first postulated by Kazimierz Kuratowski in 1922, and then independently by Zorn in 1935.
Zorn was born in Krefeld, Germany. He attended the University of Hamburg. He received his PhD in April 1930 for a thesis on alternative algebras. He published his findings in Abhandlungen aus dem Mathematischen Seminar der Universität Hamburg. Zorn showed that split-octonions could be represented by a mixed-style of matrices called Zorn's vector-matrix algebra.
Max Zorn was appointed to an assistant position at the University of Halle. However, he did not have the opportunity to work there for long as he was forced to leave Germany in 1933 because of policies enacted by the Nazis. According to grandson Eric, "[Max] spoke with a raspy, airy voice most of his life. Few people knew why, because he only told the story after significant prodding, but he talked that way because pro-Hitler thugs who objected to his politics, had battered his throat in a 1933 street fight."
Zorn immigrated to the United States and was appointed a Sterling Fellow at Yale University. While at Yale, Zorn wrote his paper "A Remark on Method in Transfinite Algebra" that stated his Maximum Principle, later called Zorn's lemma. It requires a set that contains the union of any chain of subsets to have one chain not contained in any other, called the maximal element. He illustrated the principle with applications in ring theory and field extensions. Zorn's lemma is an alternative expression of the axiom of choice, and thus a subject of interest in axiomatic set theory.
In 1936 he moved to UCLA and remained until 1946. While at UCLA Zorn revisited his study of alternative rings and proved the existence of the nilradical of certain alternative rings.