If we mean inhuman as in non-human and irrational, then def Afton. After becoming springtrap and later scraptrap his obsession with killing children becomes more like an animalistic instinct, to the point where he'll act based on it even if he knows it's a stupid thing to do, and as burntrap, he doesn't even speak anymore and is just an hate-filled beast.

@KoshaVinka You are right in what he says but I agree that William becomes more a style of villain disturbed by the death of his youngest son, plus the other three options are just as inhumane at the very least:

-Albert is an artificial human creation who eventually believed himself to be a superior being and also wanted immortality and also to dominate the world with his own race of superiors.

-Makarov ordered the explosion of a nuclear bomb that killed 30,000 marines, massacred an entire airport to start World War III, kidnapped the president of his country to get the nuclear codes and return Europe a handful of ashes, having no problem in sacrificing his men to win.

-Micah is a manipulator, savage, unpredictable, killing almost an entire town for his guns, never sleeps, never eats, shows hatred with both civilization and nature, several facets of hatred as racism, atheism, etc., but what makes him different from the rest is that he does not seem to care about dying, showing indifference and even laughing in his last moments of life.

At this point, I’m surprised William isn’t headlined yet.

Obviously It's Springtrap