Ivan Ristić
Serbian-British developer behind ModSecurity and SSL Labs, the tool that gave every HTTPS server a grade from A to F.
Ristić wrote ModSecurity in 2002 as an Apache module: an open-source WAF that checked HTTP requests against rules before they reached the application. It became the de facto free web application firewall and lives on alongside the OWASP Core Rule Set.
SSL Labs, launched in 2009 and later part of Qualys, tested a server's TLS setup — protocols, cipher suites, certificate chain, known vulnerabilities — and boiled it down to a school grade. That turned out to be a remarkably effective way to get admins to switch off SSL 3.0: nobody wants an F. He also wrote Bulletproof SSL and TLS (2014) and later founded Hardenize.