German mathematician George (Georg) Ferdinand Ludwig Philipp Cantor (1845–1918) was not only known for his work on transfinite numbers, but also for his development of the set theory, which is the basis of modern mathematical analysis (for more information on set theory, see “Foundations of Mathematics”). His *Mathematische Annalen* was a basic introduction to set theory. Unlike most long evolutionary histories of mathematical subjects, Cantor’s set theory was his creation alone. In the late 19th century, Cantor also developed the Continuum Hypothesis. He realized that there were many different sized infinities, further conjecturing that two particular infinities constructed by different processes were the same size.