Marian Adam Rejewski (16 August 1905 – 13 February 1980) was a Polish mathematician and cryptologist who reconstructed the Nazi German military Enigma cipher machine sight-unseen in 1932. The cryptologic achievements of Rejewski and colleagues Jerzy Rózycki and Henryk Zygalski enabled the British to begin reading German Enigma-encrypted messages at the start of World War II, seven years after Rejewski's original reconstruction of the machine. The intelligence that was gained by the British from Enigma decrypts formed part of what was code-named Ultra and contributed—perhaps decisively—to the defeat of Germany.