Alex Biryukov
Cryptanalyst at the University of Luxembourg behind both the slide attack and Argon2 – equally at home breaking things and building things that are hard to break.
With David Wagner, Biryukov described the slide attack in 1999. It exploits ciphers that repeat the same round function and so works regardless of how many rounds there are. A year later he, Adi Shamir and Wagner showed how to break GSM's A5/1 in real time on an ordinary PC. In 2009 came related-key attacks on AES-256 with Dmitry Khovratovich – theoretical, but uncomfortable for a cipher that was supposed to have margin to spare.
On the construction side he co-designed Argon2, which won the Password Hashing Competition in 2015 and went on to become the default recommendation for password hashing.