Cahit Arf
Cahit Arf (October 11, 1910-December 26 1997) was a Turkish mathematician. He was born in Salonika, which then was a part of the Ottoman Empire and died in Istanbul, Turkey.
He received his PhD from the University of Göttingen where he worked with Helmut Hasse. He is known for the Arf invariant of a quadratic form in characteristic 2 (applied in knot theory and surgery theory) in topology, the Hasse-Arf theorem in ramification theory, and Arf rings. He facilitated the now-celebrated visit of Robert Langlands to Turkey (now famous for the Langlands program, among many other things); during which Langlands worked out some arduous calculations on the epsilon factors of Artin L-functions.
He taught many years at Galatasaray Lisesi, and was a professor at the Middle East Technical University (METU) and Istanbul Technical University (ITU). He received a national prize for his research in applied mathematics. His mission was to revitalize Turkish mathematics; he was the father figure for the Turkish mathematics community. The Cahit Arf days are celebrated each year at METU.
Cahit Arf is regarded as the greatest Turkish mathematician of the twentieth century (the runner-up for the title could be Selman Akbulut).
See also: List of Turkish scientists