Ernst Friedrich Ferdinand Zermelo was born in Berlin on 27 July 1871. It was the time when Georg Cantor wrote his papers on trigonometric series. As Zermelo expressed it about 60 years later, these papers led with inherent necessity to the conception of transfinite ordinal numbers; they hence could be considered the birthplace of Cantorian set theory, i.e., the theory whose transformation into an axiomatic form would be an essential part of Zermelo's scientific achievements.