In 1979, Warren Robinett wrote Adventure for the Atari 2600. In addition to being the first action-adventure and console fantasy game, it's also the first video game to include an "easter egg".
A couple of commented disassemblies of the game can be found on the web. I took a moderately detailed one created by Joel D. Park and converted it to SourceGen format. (This was primarily an exercise to convince myself that the address mirroring and graphics visualizers worked correctly -- I didn't really add anything to the existing text.)
Copyright 2020 by Andy McFadden