I have already remarked upon Aristotle's enormous influence on thinking about infinity. If I had to name one other figure whose influence on the field has been prodigious, it would be Georg Cantor, the mathematician who (along with Bernard Bolzano) founded set theory, founded the theory of transfinite numbers, and was perhaps history's greatest champion for the actual infinite. Most of the standard doctrine now accepted among mathematicians and philosophers concerning infinity is taken straight from the pages of Cantor.