Klaus Friedrich Roth, Fields Medal 1958

Klaus Friedrich Roth (29 October 1925 – 10 November 2015) was a German-born British mathematician known for work on diophantine approximation, the large sieve, and irregularities of distribution. He was born in Breslau, Prussia, but was raised and educated in the UK. He was pupil at St Paul's School in London from 1939 to 1943 and then attended Cambridge University, graduating from Peterhouse, Cambridge in 1945. In 1946 he began research at University College London, under the supervision of Theodor Estermann.

cepted on to a master’s course at University College, London. Having completed his master’s, he became a lecturer there in 1950. He met his wife, Melek Khairy, after she sat in the front row of his inaugural lecture. For Roth it was love at first sight, and by the end of the year he delegated marking her papers to a colleague as he could no longer trust his impartiality. They married in 1955 and had a happy union until her death in 2002. In 1960 Roth was elected to the Royal Society and was promoted to professor the following year.

In 1952, Roth proved that subsets of the integers of positive density must contain infinitely many arithmetic progressions of length three, thus establishing the first non-trivial case of what is now known as Szemerédi's theorem. His definitive result, now known usually as the Thue–Siegel–Roth theorem, but also just Roth's theorem, dates from 1955, when he was a lecturer at University College London. He was awarded a Fields Medal in 1958 on the strength of it. He became a professor at University College London in 1961, and moved to a chair at Imperial College London in 1966, a position he retained until official retirement at 1988. He then remained at Imperial College as Visiting Professor until 1996.

The Imperial College Department of Mathematics instituted the Roth Doctoral Fellowship in his honour.