Mark Krein

Mark Grigorievich Krein was a Soviet Jewish mathematician who spent most of his career in Odessa, where antisemitic policies barred him from the most prestigious posts despite his towering reputation. He made deep contributions to functional analysis, operator theory and the moment problem, including the Krein–Milman theorem on extreme points of convex sets — a cornerstone of modern analysis. His body of work profoundly shaped the mathematics of infinite-dimensional spaces.