Worked with many great ones but the one who really stands out seemed levels above everyone in terms of just raw intelligence.

When you explain a concept to another human you have to provide context and a certain level of detail. It can be hard to calibrate based on who you talk to. What always blew me away about this guy was he needed like almost 0 context, even for non-programming subjects. He understood within seconds what you were doing, even for complex problems. I had to recalibrate my entire approach to explanation with him because he got things instantly.