Martin Hellman
lorecryptographysecurity
Co-author of New Directions in Cryptography and of the key-exchange method that carries his name with Diffie's; joint recipient of the 2015 Turing Award.
His citation is worth reading closely: it credits inventing AND promulgating, which is the pair of verbs this history keeps requiring. The exchange lets two parties agree a shared secret over a channel someone else is listening to, and it is still the thing happening at the start of a TLS session decades later - which is why forward secrecy is available at all. He spent much of his later career on nuclear risk rather than cryptography, which the record should mention rather than tidy away.
Also known as: hellman