Leopold Kronecker

Leopold Kronecker was born in Prussia on 7 December 1823 and trained under Ernst Kummer, forging a friendship that lasted until the end. He built his reputation on number theory, abstract algebra, and logic, insisting mathematics stay grounded in the concrete and the countable. That conviction put him on a collision course with Georg Cantor, whose work on set theory Kronecker criticized as overreach — a war of philosophies that defined late 19th-century mathematics. He died 29 December 1891, having drawn a line in the sand: integers were divine, everything beyond them mere human construction.