Answer: Diablo II
Back in the mid-1990s, when players were hacking and slashing their way through Diablo Blizzard Entertainment's smash hit action RPG adventure, there was a persistent rumor that was continuously retold and recirculated among fans: if you clicked on a certain cow in the city of Tristam a specific number of times, a magical portal would open up and you could access super secret level where there was nothing but cows. There was, however, no secret cow level in Diablo .
The rumor was so persistent and blizzard was so frequently asked about it that, as a joke, they included a cheat code in StarCraft : "there is no cow level". Still, the rumors persisted, and even after no one was able to uncover the secret cow level, fans of the franchise kept the joke going with frequent discussions online about how awesome a cow level would be.
Shortly after the release of Diablo II in 2000, fans of the franchise finally got their wish. An Easter egg was uncovered: by assembling the proper quest items and jumping through a few in-game hoops, you could, in fact, open up a magic portal to a magical land filled with thousands upon cows and their cow king, all of which dropped copious amounts of gold and other loot (until later on the amount of rewards that could be obtained).
Years later, in 201