ANSI C - K&R
This is not my first go-round in C. C is what I originally learned when I was 10, trying to make text adventure games with my dad.
I used it throughout middle and high school, and destroyed C programming classes in college while getting my electrical engineering degree. But at some point in college, I started to focus on SaaS products and my life drifted toward JS. I've picked up a few languages here and there, Lisp, Go (though not in production), advanced up to TypeScript - but I want to get back to my roots!
So I've returned to the first real programming book I ever learned from to see what I have to learn.
I just listened to an interview with one of the authors. Let's go baby.