Richard Feldman is a US software engineer and the creator of Roc (a fast functional programming language), a long-running Elm community member, and the author of Elm in Action (Manning). His teaching style is unusually rigorous about the theoretical underpinnings of programming languages and the design decisions that shape them.
His CourseFlix listing carries two Richard Feldman courses: Building a Static Type-Inferring Compiler (a from-scratch implementation of a Hindley-Milner-style type inferring compiler) and C Fundamentals (the foundational C course). Both reflect Richard's depth on the systems-and-language-implementation end of programming.
Material is paid and aimed at engineers ready to study programming languages from the implementation side. For broader content, see CourseFlix's Compilers & Interpreters and C++ category pages.