Josip Plemelj (December 11, 1873 – May 22, 1967) was a Slovene mathematician, whose main contributions were to the theory of analytic functions and the application of integral equations to potential theory. He was the first chancellor of the University of Ljubljana.
Plemelj was born in the village of Bled near Bled Castle in Austria-Hungary (now Slovenia); he died in Ljubljana, Yugoslavia (now Slovenia). His father, Urban, a carpenter and crofter, died when Josip was only a year old.
His mother Marija, née Mrak, found bringing up the family alone very hard, but she was able to send her son to school in Ljubljana where Plemelj studied from 1886 to 1894. Due to a bench thrown into Tivoli Pond by him or his friends, he could not attend the school after he finished the fourth class and had to pass the final exam privately.
After leaving and obtaining the necessary examination results he went to Vienna in 1894 where he had applied to Faculty of Arts to study mathematics, physics and astronomy. His professors in Vienna were von Escherich for mathematical analysis, Gegenbauer and Mertens for arithmetic and algebra, Weiss for astronomy, Stefan’s student Boltzmann for physics.
In May 1898, Plemelj presented his doctoral thesis under Escherich’s tutelage entitled O linearnih homogenih diferencialnih enačbah z enolično periodičnimi koeficienti (Über lineare homogene Differentialgleichungen mit eindeutigen periodischen Koeffizienten, About linear homogeneous differential equations with uniform periodical coefficients).
He continued with his study in Berlin (1899/1900) under the German mathematicians Frobenius and Fuchs and in Göttingen (1900/1901) under Klein and Hilbert.
In April 1902 he became a private senior lecturer at the University of Vienna. In 1906 he was appointed assistant at the Technical University of Vienna. In 1907 he became associate professor and in 1908 full professor of mathematics at the University of Chernivtsi (Russian Черновцы), Ukraine. From 1912 to 1913 he was dean of this faculty. In 1917 his political views led him to be forcibly ejected by the Government and he fled to Bohemia (Moravska).
After the First World War he became a member of the University Commission under the Slovene Provincial Government and helped establish the first Slovene university at Ljubljana, and was elected its first chancellor. In the same year he was appointed professor of mathematics at the Faculty of Arts. After the Second World War he joined the Faculty of Natural Science and Technology (FNT). He retired in 1957 after having lectured in mathematics for 40 years.