Georg Cantor, a German mathematician, developed a number of ideas that profoundly influenced 20th-century mathematics. Among other accomplishments, he introduced the idea of a completed infinity, an innovation that earned him recognition as the founder and creator of set theory. His revolutionary insights, however, were accepted only gradually and not without opposition during his lifetime. The praise for his work was best epitomized by the famous mathematician David Hilbert, who said that "Cantor has created a paradise from which no one shall expel us." Besides being the founder of set theory, Cantor also made significant contributions to classical analysis. In addition, he did innovative work on real numbers and was the first to define irrational numbers by sequences of rational numbers.

Georg Ferdinand Ludwig Philipp Cantor was born on March 3, 1845, in St. Petersburg, Russia, the first child of Georg Woldemar Cantor and Maria Böhm. The family...