Peter Christian Julius Petersen
Born: June 16, 1839 in Sorø, Denmark
Died: August 5, 1910 in Copenhagen, Denmark
Julius Petersen's fame rests primarily upon a single paper written in 1891 entitled Die Theorie der regulären graphs. Today we recognize this publication as one of the first, if not the first, containing fundamental results on the theory of graphs.
As a professor at the University of Copenhagen Petersen visited J. J. Sylvester in Oxford. The two had collaborated extensively but decided to publish separately. Sylvester was the first to use the term "graph" as it is used today but Petersen's paper gave the field a foundation that was finally accepted by mathematicians.