Niels Provos
German security researcher who gave the world bcrypt, privilege separation in OpenSSH and honeyd.
In 1999 Provos and David Mazières presented bcrypt, a password hash with a tunable cost factor that can be made slower as hardware gets faster. It became the default in OpenBSD and remains a sensible choice a quarter of a century later, which is rare in cryptography.
For OpenSSH he introduced privilege separation (2002): the part that talks to the network runs unprivileged, so a bug there doesn't hand over root. He also wrote honeyd, which simulates entire networks of honeypots, and the systrace sandboxing tool. At Google he mapped websites serving malware, work that fed into Safe Browsing, and he later became head of security at Stripe.