Félix Delastelle
French cryptographer who invented the Bifid and Trifid ciphers at the turn of the twentieth century.
Delastelle (1840–1902) was a French cryptographer and writer who set out his field in Traité élémentaire de cryptographie (1902). He invented the Bifid cipher in 1901 and the Trifid cipher in 1902. Both rely on fractionation: each plaintext letter is split into parts that are then recombined by transposition, which blunts simple frequency analysis. They still need a grid and careful handling, but they were a clear step beyond plain substitution.