Damien Miller
Australian developer who since 1999 has made sure OpenBSD's SSH implementation works on every other system too.
OpenSSH was written for OpenBSD, and its developers wanted the code free of portability clutter. Miller took on portable OpenSSH, a separate tree with compatibility shims for Linux, macOS, Solaris and the rest. That is the version running on practically every server in the world.
The split — a clean core in OpenBSD, adaptations in a layer of their own — became the template for other OpenBSD projects such as LibreSSL and OpenNTPD. Miller has been among OpenSSH's most active developers for a quarter of a century, following the project all the way to post-quantum key exchange by default: sntrup761 in 9.0 (2022), ML-KEM in 10.0 (2025).