Gösta Mittag-Leffler (1846-1927) played a significant role as both a scientist and entrepreneur. Regarded as the father of Swedish mathematics, his influence extended far beyond his chosen field because of his extensive network of international contacts in science, business, and the arts. He was instrumental in seeing to it that Marie Curie was awarded the Nobel Prize twice. One of Mittag-Leffler's major accomplishments was the founding of the journal Acta Mathematica , published by Institut Mittag-Leffler and Sweden's Royal Academy of Sciences. Arild Stubhaug's research for this monumental biography relied on a wealth of primary and secondary resources, including more than 30000 letters that are part of the Mittag-Leffler archives. Written in a lucid and compelling manner, the biography contains many hitherto unknown facts about Mittag-Leffler's personal life and professional endeavors. It will be of great interest to both mathematicians and general readers interested in science and culture.