Eugene Grebenik CB (Ukrainian: Євген Гребеник; 20 July 1919 – 14 October 2001), known as "Grebby", was a British civil servant who was a central figure in the development of demography in Britain.

He was the only son and elder child of Jewish parents Schulim Grebenik (1887–1972), estate agent, and his wife, Lea Helene (née Lopatizkaya; 1894–1985), a qualified lawyer.

Rejected by the army due to his foreign birth, Grebenik returned to the LSE in 1940 and graduated MSc in 1941.

His work with Glass on the 1946 family census, published in two volumes as The Trend and Pattern of Fertility in Great Britain (1954), was a landmark in cohort analysis.

He left the college in 1976 to conduct research at the Office of Population Censuses and Surveys, working with Abraham Manie Adelstein and John Fox, where he remained until he retired in 1984.