Fabrice Bellard (who also had some spare time to create ffmpeg, QEMU, and a few others like a software implementation of a 4G-LTE base station) wrote tcc, the tiny C compiler: https://bellard.org/tcc/

Small, fast and of course self-compiling! The project is the better compiler out of a first project named OTCC which won the IOCCC (yes, the obfuscated C programming contest - less than 2k bytes). https://bellard.org/otcc/