From Diablo Wiki
Easter Eggs are bonus features in hidden in many types of software and electronics products. Wikipedia defines them as:
- Easter eggs are messages, videos, graphics, sound effects, or an unusual change in program behavior that sometimes occur in a software program in response to some undocumented set of commands, mouse clicks, keystrokes or other stimuli intended as a joke or to display program credits.
Blizzard Entertainment is notorious for including amusing Easter Eggs in their products, including all of the games in the Diablo series.
Diablo Easter Eggs
This wiki contains articles that document the Easter Eggs in all three Diablo games.