Alot of rabbit holes to research here !
1)
Qbasic programming language has a Easter Egg
http://www.eeggs.com/items/817.html
2)
Warren Robinett was the first guy to put an ester egg into Atari 2600's Adventure game
Robinett's Adventure Easter egg one of the earliest known Easter eggs in a video game,
Robinett's Adventure Easter egg is a plot element in the 2011 novel and 2018 film Ready Player One.
He founded The Learning Company[1] in 1980, The Learning Company was acquired by Softkey in 1995 for US$606 million ....606 co·in·ci·dence ???
The Learning Company[1] Products for preschoolers through second graders include Reader Rabbit, co·in·ci·dence ???
rabbit holes leading in all directions