Carl Hierholzer (2 October 1840 – 13 September 1871[1]) was a German mathematician.
Hierholzer studied mathematics in Karlsruhe, and he got his Ph.D. from Ruprecht-Karls-Universität Heidelberg in 1865.
In 1870 Hierholzer wrote his habilitation about conic sections (title: Ueber Kegelschnitte im Raum) in Karlsruhe, where he later became a Privatdozent.
Hierholzer proved that a connected graph has an Eulerian trail if and only if exactly zero or two of its vertices have an odd degree.
Hierholzer apparently presented his work to a circle of fellow mathematicians not long before his premature death in 1871.