Gyula Kőnig (16 December 1849 – 8 April 1913) was a mathematician from Hungary. His mathematical publications in German appeared under the name Julius König. His son Dénes Kőnig was a graph theorist. Biography Gyula Kőnig was active literarily and mathematically. He studied medicine in Vienna and, from 1868 on, in Heidelberg. After having worked, instructed by Hermann von Helmholtz, on electrical stimulation of nerves, he switched to mathematics. He obtained his doctorate under the supervision of the mathematician Leo Königsberger. His thesis Zur Theorie der Modulargleichungen der elliptischen Functionen covers 24 pages. As a post-doc he completed his mathematical studies in Berlin attending lessons by Leopold Kronecker and Karl Weierstraß. He then returned to Budapest where he was appointed as a dozent at the University in 1871. He became a professor at the Teacher's College in Budapest in 1873 and, in the following year, was appointed professor at the Technical University of Budapest. He remained with the university for the rest of his life. He was on three occasions Dean of the Engineering Faculty and also on three occasions was Rector of the University. In 1889 he was elected a member of the Hungarian Academy of Sciences. Although of Jewish descent, Kőnig converted to Christianity soon after his election. In 1905 he retired but continued to give lessons on topics of his interest. His son Dénes also became a distinguished mathematician. Works Kőnig worked in many mathematical fields. His work on polynomial ideals, discriminants and elimination theory can be considered as a link between Leopold Kronecker and David Hilbert as well as Emmy Noether. Later on his ideas were simplified considerably, to the extent that today they are only of historical interest. Kőnig already considered material influences on scientific thinking and the mechanisms which stand behind thinking. But mainly he is remembered for his contributions to and his opposition against set theory. Kőnig and set theory One of the greatest achievements of Georg Cantor was the construction of a one-to-one correspondence between the points of a square and the points of one of its edges by means of continued fractions. Kőnig found a simple method involving decimal numbers which had escaped Cantor. In 1904, at the third International Congress of Mathematicians at Heidelberg, Kőnig gave a talk to disprove Cantor's continuum hypothesis. The announcement was a sensation and was widely reported by the press. All section meetings were cancelled