Klaus Roth

Klaus Friedrich Roth (1925 to 2015) was a mathematician born in Breslau, then in Germany and now Wrocław in Poland, who came to England as a boy and spent his working life in Britain. He attended St Paul's School in London, took his first degree at Peterhouse, Cambridge in 1945, taught for a time at Gordonstoun School in Scotland, and then returned to London for research at University College, where he earned his doctorate, became a reader in 1956 and a professor in 1961. In 1966 he moved to the chair of pure mathematics at Imperial College. Roth is remembered above all for the 1955 result that closed the long search for how well an algebraic irrational number can be approximated by rational numbers, a question that Liouville, Thue and Siegel had each narrowed before him. The work won him a Fields Medal in 1958, presented by Harold Davenport at the International Congress in Edinburgh. He also proved in 1952 a conjecture of Erdős and Turán of 1935 about sequences of natural numbers that avoid a particular additive equation. Roth died in Inverness, Scotland, in 2015.