Karl F. Sundman
Karl Frithiof Sundman (28 October 1873, in Kaskinen – 28 September 1949, in Helsinki) was a Finnish mathematician who used analytic methods to prove the existence of a convergent infinite series solution to the three-body problem in two papers published in 1907 and 1909. His results gained fame when they were reproduced in Acta Mathematica in 1912. He also published a paper on regularization methods in mechanics in 1912.