5 Rumors That Made An Impact - VGFacts Five Trivia
There was almost a Nintendo 64/64DD release. However, Nintendo had no information regarding which console, at the time, would have the game.
Contributed by GamerBen144
In the Hellfire DLC, adding a commmand.txt file to the Hellfire folder will change Na-Krul's usual dialogue to that of an Aerosmith announcer:

Hi! I'm free, free to confront the little man who banished me, Diablo. Hi, everybody, and I'm free to reward you, little mortal, with these Aerosmith tickets. You'll be getting backstage passes, you'll get to meet Steven Tyler and the whole band. This Friday at the Coliseum. Thanks for getting me out of there. By the way, I'm gonna have to kill you. (pause)

I'll be right back with the traffic and weather together.
Contributed by ThisGuyInTheSuit
Character Classes were late additions to the game. Originally, there was only a single class, represented by the warrior's model. Players could distribute their experience points between their stats to make the character to their liking.
Contributed by ThisGuyInTheSuit
Diablo was at one point also being developed for the Game Boy but was later canceled for unknown reasons. A tech demo was produced but had never been shown to the public.
Contributed by KnowledgeBase
The Butcher originally had a pre-rendered cinematic that would play when first encountered. It is left on the disk, but goes entirely unused.
Contributed by Dazz
If you recolor a part of the Diablo boot screen you will find a hidden message from the game's developers about Natalie Portman and "War II".
Contributed by DidYouKnowGaming
When the demonic boss "Diablo" is released in the final level, he says something in a bizarre language. When played in reverse, the voice is in English, and says "eat your vegetables and brush after every meal."
Contributed by DidYouKnowGaming