To me, SHODAN is an amazing piece of artistry, the best villain I’ve been terrified by in many, many games. Her initial curiosity, hatred then abuse is great, and the way her audio cues come in are very effective in browning pants.
What other villains come close to this?
“In my talons, I shape clay, crafting life forms as I please. If I wish, I can smash it all. Around me is a burgeoning empire of steel. From my throne room, lines of power careen into the skies of Earth. My whims will become lightning bolts that raze the mounds of humanity. Out of the chaos, they will run and whimper, praying for me to end their tedious anarchy. I am drunk with this vision. God: the title suits me well.”
It was also timing – the voice support allowed a lot more personality to be injected which would not have been possible previously. The Guardian from the later Ultima games is a possible contender from around that era.
Kane from the Command and Conquer series.
Also, not a singular character but the Kilrathi from the Wing Commander games got fleshed out quite well through the series