Ron Milner was a programmer working for the Atari think-tank between 1973 and 1985. He programmed the game Starship 1 and said the following to Ed Fries:
“That was the first and only game that I ever programmed and I think it was maybe one of the first games with a backdoor in it. I didn’t tell people about this, even within Atari, for at least 30 years, but I had some code in there that if you did a certain sequence of controls it would say ‘Hi Ron!’ and give you 10 free games.”
I was kind of stunned. If this was true it would certainly predate the earliest video game Easter egg that I knew of and the one that is most often cited as being the first: “Adventure” for the Atari 2600 from 1979.
Another game often cited as the first Easter egg is a game for the Fairchild from 1978. So Starship 1 would beat those since Ed discovered proof that it was released in August 1977.
I strongly encourage you to read the full post since it’s quite an endavour that Ed has gone through and quite interesting if you love old video games and programming!