1845–1918 · German mathematician, founder of set theory
Georg Ferdinand Ludwig Philipp Cantor was born in 1845 and spent his career at Halle, where he created set theory almost single-handedly. He established the one-to-one correspondence as the test of sameness of size, proved that the real numbers are more numerous than the natural numbers, and showed that this implies an endless hierarchy of infinities — results that a substantial part of the profession, led by Kronecker, refused to accept in his lifetime. He was a devout Lutheran who took the theological stakes of the actual infinite seriously, corresponded about them with Catholic scholars, and whose recurring bouts of depression, from 1884 to the end of his life, have been blamed on the hostility of his contemporaries. He died in 1918.