Horst Feistel was one of the first non-military researchers in the field of cryptography and can be considered the father of modern block ciphers.
In 1973 he published an article with the title 'Cryptography and Computer Privacy' in a magazine called 'Scientific American', in which he tried to cover the most important aspects of machine encryption and introduced what is today known as the 'Feistel Network'.
The Feistel Network later became the basis for many encryption schemes, among them the Data Encryption Standard(DES) is the most popular one.
Horst Feistel was born in Berlin in 1915 and moved to the USA in 1934, where he was placed under house arrest from 1939 until the end of World War 2 in 1945.
Nevertheless he became a US citizen in 1944 and started his scientific career at the US Air Force Cambridge Research Center where he worked on the topic of Friend or Foe Identification. Feistel obtained his Master degree in physics at Harvard and reached the peak of his success in the 1970s at IBM where he was part of the group that developed ‘Lucifer’.
‘Lucifer’ was the code name for a bunch of early block ciphers developed for civilian use. Although ‘Lucifer’ was rather a scientific project than a big commercial success, the Feistel Network which can be seen as the most striking result of this project was one of the biggest inventions in modern cryptography and became the basis of the Data Encryption Standard in 1977.
You can find Horst Feistel's Article "Cryptography and Computer Privacy" published in "Scientific American", 1973, under the following link: