Johannes Trithemius
German abbot (1462–1516) who wrote the first printed book on cryptography and coined the word steganography.
As abbot of Sponheim, Trithemius built one of Europe's great monastic libraries and wrote on everything from history to magic. Polygraphia, printed posthumously in 1518, introduced the tabula recta — the table that made polyalphabetic encryption mechanical — along with an "Ave Maria cipher" that swapped each letter for a word, so the secret message read like a pious prayer.
Steganographia, written around 1499, had a rougher ride. It appeared to be about sending messages with the help of angels, circulated in manuscript for a century, was printed in 1606 and landed on the papal Index of Forbidden Books in 1609. Only in 1998 did two researchers independently show that its third book was cryptography too — the "magical" numbers were ciphers. The occultism, in other words, was camouflage.