Legend has it that the 1979 Atari 2600 game, Adventure, was the first to include a hidden in-joke buried away in an obscure corner of the code. If players directed a grey dot into a hidden room they got to see the message “Created by Warren Robinett”, a self-referential protest by the game’s programmer who was annoyed at Atari for not crediting its staff. Since then, it’s been discovered that the Fairchild Channel F console, launched in 1976, boasted several such messages. The demo cartridge that originally came with the machine had one, as did the 1978 title Video Whizball, a Pong derivative that would post the coder’s name on the screen (Bradley Reid-Selth) if you carried out a complex sequence of moves at the close of the game.

http://www.theguardian.com/technology/2015/apr/02/12-greatest-video-game-easter-eggs