Klaus Friedrich Roth was born on October 29, 1925, and died on November 10, 2015.
He was a German-born British mathematician known for work on diophantine approximation, the large sieve, and irregularities of distribution.
Klaus was born in Breslau, Prussia, into a Jewish family, but was raised and educated in the UK, where the family settled in 1939.
He was a 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 Klaus began research at University College London, under the supervision of Theodor Estermann.
In 1952, Klaus 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.
Klaus 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 in 1988.
Klaus then remained at Imperial College as Visiting Professor until 1996.
The Imperial College Department of Mathematics instituted the Roth Doctoral Fellowship in his honour.
Klaus passed away at age 90 in November 2015.