Polish mathematician who was the younger brother of Frigyes Riesz. Educated in Budapest, Riesz was singled out for his innovative work when he won the Lorand Eotvos competition in 1904. He published only one paper with his brother, Frigyes, on boundary behavior of an analytic function but worked with others in joint research projects. In 1908, he was contacted by Mittag-Leffler in Sweden to teach and research there. He was appointed to a position in Stockholm and chaired a mathematics department at Lund. Riesz spent the rest of his life in Sweden and died in Lund in 1969.