In 1988, a piece of C code called xmas.c won the International Obfuscated C Code Contest. The code, which compresses a text to represent a new departure in text compression standards, was written by Landon Curt Noll and Larry Bassel. The code appears to be complex and difficult to understand at first glance, but after decoding and analyzing it, it turns out to be a program that prints the lyrics of the song “The Twelve Days of Christmas”. The code uses recursion and a substitution cipher to achieve this. This clever use of code and cryptography is what makes it impressive.
https://udel.edu/~mm/xmas/