Born Darmstadt, November 26, 1924. Died London, November 30, 2008, aged 84.
A self-taught mathematician, Professor John Hajnal first made his name in demography and had a marriage phenomenon named after him.
A precocious intellectual and linguist, he never stopped scooping up knowledge. Though from an unobservant home, he became interested in religious ideas.
In 1936 his Hungarian-born parents left Germany where, as a Jew, he had been made to sit at the back of the class, and placed him in a Quaker school in the Dutch countryside while they arranged to settle in Britain.
Reunited with his parents and two younger sisters in 1937 — nearly all his Jewish classmates in Holland perished in the Holocaust — John went to University College School, Hampstead, and at 16 went straight on to Oxford.
Though his natural bent was maths and science, his school had steered him into classics. He switched to politics, philosophy and economics, gaining a first in 1943.
His first job, with the Royal Commission on Population, led to his being recruited in 1948 to work at the UN in New York on demography.
At a barmitzvah party in New York for the son of friends of his parents, he met vivacious Berlin-born Nina Lande. They married in 1950. Frustrated by his lack of mathematical background, he left full-time employment to catch up on academic maths, while his wife taught and had their first child.
In 1953 he returned to England as a medical statistician in Manchester. The family moved to London in 1956 when John secured a lectureship at the London School of Economics, on the strength of his earlier demographic research and output.
Gradually moving across to theoretical statistics, he was promoted reader in 1966, the same year that he was elected to the British Academy, and became professor of statistics in 1975. He had visiting professorships at Cambridge and in the US and retired in 1986.
Though fundamentally shy, he was deeply family-oriented and always interested in people and their cultural and religious sensibilities .
He was an expert on Markov chains, a random series used in sampling, and in 1965 discovered the Hajnal Line, named after him, a line from Russia’s north-west coast moving south-east to Trieste, which historically separated early marriages with more children in the east from later marriages and smaller families in the west.
His wartime experience gave a moral edge to his incisive, analytical mind and he abhorred the seduction of the intellect in others by ideologies such as post-war Communism.
Suffering from lymphoma, he was predeceased by his wife seven months before his own death and is survived by three daughters, a son and three grandchildren.