Ken Thompson interviewed by Brian Kernighan at VCF East 2019 (min 39, sec 46)

https://youtu.be/EY6q5dv_B-o?t=2386

Describes how Douglas McIlroy designed a language, wrote a compiler in the language that he designed that didn't exist yet and hand converted this compiler to assembly. Ken Thompson says it's one of the most impressive things he's ever seen in his life.