Establishing Stalin's Birthdate, Wikipedia: Joseph Stalin

Although there is an inconsistency among published sources about Stalin's year and date of birth, Iosif Dzhugashvili is found in the records of the Uspensky Church in Gori, Georgia as born on 18 December (Old Style: 6 December) 1878. This birth date is maintained in his School Leaving Certificate, his extensive tsarist Russia police file, a police arrest record from 18 April 1902 which gave his age as 23 years, and all other surviving pre-Revolution documents. As late as 1921, Stalin himself listed his birthday as 18 December 1878 in a curriculum vitae in his own handwriting. However, after his coming to power in 1922, Stalin changed the date to 21 December 1879 (Old Style date 9 December 1879). That became the day his birthday was celebrated in the Soviet Union."Prominent figures". State and Power in Russia. http://state.rin.ru/cgi-bin/persona_e.pl?id=4140&id_subcat=6&r=8. Retrieved 19 July 2008.