Rasch was the son of a mathematics teacher who ran a mission high school for prospective seamen. He gained his first taste for mathematics through reading his father's trigonometry textbooks. He graduated in mathematics at U Copenhagen in 1925, obtaining his PhD in 1930. His subsequent work as a consultant brought him into contact with Statistics. In 1934 he joined Sir Ronald Fisher in London. He returned to Denmark in 1935 to the Bio-Statistical Department of the Danish National Serum Laboratory. In 1947 he was a founder member of the IBS. In 1961 he returned to U Copenhagen as Professor of Statistics. His work on the Rasch model was published in 1960. He became a Danish knight in 1967.

http://www.rasch.org/olsen.pdf Biographical PhD thesis with photograph.