Julius Petersen [1839 - 1910] wrote on a wide variety of mathematical topics throughout his career. His dissertation concerned geometric constructability, but he also published work on differential equations, analysis, number theory, algebra, and even such applied topics as mathematical economics and cryptography.
He is best remembered for his pioneering work in graph theory; his 1891 paper on the theory of regular graphs has been cited as the beginning of graph theory as a discipline. His 10 vertex graph, known simply as The Petersen Graph, is “the smallest bridgeless cubic graph with no three-edge-coloring“, and has become one of the standard (counter)examples studied in introductory graph theory courses.
Mathematicians with birthdays or death anniversaries during the week of June 15 through June 21:
June 15: Birthday of Nikolai Chebotaryov  (generalized Dirichlet’s theorem on primes in arithmetic progressions); death of Giovanni Ceva  (Ceva’s Theorem)
June 16: Birthdays of Julius Plücker  (analytic geometry), Julius Petersen  (Petersen graph), and John Tukey  (fast fourier transform); death of Julius Weingarten  (theory of surfaces)
One wonders if John Tukey’s parents had considered the name “Julius”.
June 17: Birthday of Maurits Escher  (artist); death of Frank Yates  (statistics; design of experiments)
June 18: Birthdays of Frieda Nugel  (one of the first German women to earn a PhD in Mathematics [in 1912]) and Alice Schafer  (differential geometry; founding member of AWM); death of Kazimierz Kuratowski  (topology)
June 19: Birthday of Blaise Pascal  (pioneer of probability)
June 20: Birthday of Helena Rasiowa  (interactions of algebra and logic)
June 21: Birthday of Siméon-Denis Poisson  (influential work on definite integrals and trigonometric series); death of Gaston Tarry  (combinatorics; results on magic squares)