Poster A-Yty of The CV Dungeon Forums asked this question and I thought it'd be worthwhile to ask it here as well.
I wouldn't mind getting two answers (one for the computer side, another for consoles, or preferably one for RPGs and another for action games).
So far we have Tau Ceti, a 1985 computer game, and Castlevania II from 1988 (Ultima V was also from 1988, a bit too late to take a distinction of being earlier from Castlevania).
Anything earlier come to mind?