|Died||11 October 1996 (aged 89)|
|Alma mater||University of Helsinki|
|Known for||Riemann surfaces, quasiconformal mappings, Denjoy-Carleman-Ahlfors theorem, Ahlfors finiteness theorem for Kleinian groups, Ahlfors theory, Conformal geometry, Geometric function theory|
|Awards||Fields Medal (1936)|
Wihuri Prize (1968)
Wolf Prize (1981)
Leroy P. Steele Prize (1982)
|Institutions||University of Helsinki|
|Doctoral advisor||Ernst Lindelöf|
|Doctoral students||Paul Garabedian|
Albert Marden (de)
Ahlfors was born in Helsinki, Finland. His mother, Sievä Helander, died at his birth. His father, Axel Ahlfors, was a professor of engineering at the Helsinki University of Technology. The Ahlfors family was Swedish-speaking, so he first attended a private school where all classes were taught in Swedish. Ahlfors studied at University of Helsinki from 1924, graduating in 1928 having studied under Ernst Lindelöf and Rolf Nevanlinna. He assisted Nevanlinna in 1929 with his work on Denjoy's conjecture on the number of asymptotic values of an entire function. In 1929 Ahlfors published the first proof of this conjecture, now known as the Denjoy-Carleman-Ahlfors theorem. It states that the number of asymptotic values approached by an entire function of order ? along curves in the complex plane going toward infinity is less than or equal to 2?.
He completed his doctorate from the University of Helsinki in 1930.
Ahlfors worked as an associate professor at the University of Helsinki from 1933 to 1936. In 1936 he was one of the first two people to be awarded the Fields Medal (the other was Jesse Douglas). In 1935 Ahlfors visited Harvard University. He returned to Finland in 1938 to take up a professorship at the University of Helsinki. The outbreak of war led to problems although Ahlfors was unfit for military service. He was offered a post at the Swiss Federal Institute of Technology at Zurich in 1944 and finally managed to travel there in March 1945. He did not enjoy his time in Switzerland, so in 1946 he jumped at a chance to leave, returning to work at Harvard where he remained until he retired in 1977; he was William Caspar Graustein Professor of Mathematics from 1964. Ahlfors was a visiting scholar at the Institute for Advanced Study in 1962 and again in 1966. He was awarded the Wihuri Prize in 1968 and the Wolf Prize in Mathematics in 1981. He served as the Honorary President of the International Congress of Mathematicians in 1986 at Berkeley, California, in celebration of his 50th year of the award of his Fields Medal
His book Complex Analysis (1953) is the classic text on the subject and is almost certainly referenced in any more recent text which makes heavy use of complex analysis. Ahlfors wrote several other significant books, including Riemann surfaces (1960) and Conformal invariants (1973). He made decisive contributions to meromorphic curves, value distribution theory, Riemann surfaces, conformal geometry, quasiconformal mappings and other areas during his career.