Patrick Wardle
A macOS security researcher who founded the Objective-See Foundation and publishes free Mac security tools alongside his vulnerability research.
Patrick Wardle is probably the best known independent researcher working on Mac security. He runs the Objective-See Foundation, which gives away Mac security tools for free, and he wrote The Art of Mac Malware, a reference for how attacks on macOS actually work. When something goes wrong in a Mac application in a way that matters, he is often the person who finds it and explains it publicly.
His usual method is to publish the flaw together with a working proof of concept, a small program that demonstrates the problem is real rather than theoretical. That is a debated practice, since it hands the technique to everybody, but the argument for it is that vendors move faster when the evidence is public and users can see for themselves what the risk is.