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.