If I had to guess, I’d he’s become disillusioned with “real” people–why else would anyone go to that amount of effort and trouble to create such realistic AI’s if not because they find the real world and its people so repugnant?
This is a crackpot theory, but I wonder if, from the Director’s perspective, the park is actually there for the androids rather than the humans in that it’s a petri dish of sorts for producing AI self-awareness. Like the Director is actually trying to achieve something like the Singularity, and in order to do that, he needs to create an artificial/accelerated evolutionary milieu. That line about “you are the most real when you’re suffering” from the Man in Black might be foreshadowing the idea that self-awareness is achieved as a result of suffering.
He seems more of the monster in a nightmare; he’s the dark mirror that is held up to humanity–here be dragons sort of metaphor for what happens when humans are allowed to give into their darkest and deepest desires.
I think what’s so utterly terrifying about him is this sense of self-absorbed ennui. His entire quest for the maze seems like this last ditch attempt to alleviate his boredom, and that sense of entitled nihilism is what’s so completely monstrous about him.