Just look at his 2001 winning International Obfuscated C Code Contest self-hosting C compiler: http://www0.us.ioccc.org/2001/bellard.hint
He won the year before too, with a program which found the largest known prime number.
In 2009 he wrote a program which he used to calculated Pi to the most digits ever (at that point), on a desktop PC. He broke the previous record which was set on a 640 nodes supercomputer.
(Oh yes, original author of QEMU and FFMPEG too)