Felix Delastelle

Felix Marie Delastelle (1840–1902) was a Frenchman most famous for his invention of several systems of polygraphic substitution ciphers including the bifid, trifid, and the four-square ciphers.

Delastelle's work on the four-square cipher was published in a book in 1901, though some of Delastelle's ideas were anticipated by an American mathematician and astronomer named Pliny Chase in 1859.