The very first video game “easter egg” occurred in Adventure for the Atari 2600.
Players had to use the magic bridge in the maze to get an otherwise unobtainable and partly invisible dot. When that dot is placed in the room with a normally impenetrable black line, the player can then cross the line into the next room which contains... (wait for it) … vertical text that reads “Created by Warren Robinett”
Because Atari had a policy of not crediting their programmers. Yup kids, it was a different era.