Math genealogy says Bernhard Riemann received the
Dr. phil. degree in 1851 from
Georg-August-Universität, Göttingen.
His advisor was C. F. Gauß .
Dissertation title: "Grundlagen für eine allgemeine Theorie der Funktionen einer veränderlichen complexen Größe"
Trans: "Foundations for a general theory of functions of a variable complex quantity"