Set theory, which was developed by Gorge Cantor (1845-1918) between 1874-1895, is a basic mathematical tool that is used by various branches of mathematics such as Group Theory, Topology, Probability Theory, Calculus, Geometry, etc. Cantor was born in Russia in 1845, but moved to Germany in 1856. In 1863 he entered the University of Berlin, where he studied under K. Weierstrass (1815-1897), L. Kronecker (1823-1891), and E.E. Kummer (1810-1893), all of whom are famous mathematicians, and received his Ph.D in 1867. One of the subsequent main works in set theory is by F. Hausdorff, which was first published in 1914.