My favourite story of Diablo's development (as relayed by David Brevik in the Diablo Postmortem - see below) is the part where Diablo was made real-time. He passionately championed that it should be more like Rogue or Moria purely turn-based and permadeath. That was until he implemented real-time movement in an afternoon and attacked a skeleton. This was a directive from Blizzard, and it effectively created the ARPG genre.
https://www.youtube.com/watch?v=VscdPA6sUkc
and for those averse to Google: https://www.gdcvault.com/play/1023469/Classic-Game-Postmorte...