A cryptographer who worked at IBM in the 70s. While creating a cipher for IBM, he invented a new method of designing such ciphers, now known as Feistel Ciphers or Feistel Networks. This culminated in the designs of Lucifer and later DES, which was designated for use by the US Government for securing non-classified data for 25 years (1977-2002), and is and was used around the world for securing commercial and personal traffic, including many banks.

DES has finally been replaced by Rijndael, which won a competition out of 15 different ciphers to become the AES (Advanced Encryption Standard). Interestingly enough, Rijndael is not a Feistel cipher.