I remember going to a talk by David Brevik at NZGDC where he not only explained that the majority of Diablo was written in assembly, but that it was originally turn based, and his staff kept whining and whining about how good it would be if it were real-time. So in one weekend he made the necessary changes (ie run 1 turn/x time), ran over to a skeleton and hit it with his sword; he was sold!

I'm sure he tells the story in that format a lot but it was still awesome hearing it from the man himself.

Wait is it now known as something other than an RPG?

I've always regarded it as a real-time roguelike. In fact it's probably the first game I played and thought, "this is like Rogue."