Crusher.
An amalgamate made out of the destruction the atomic war made between the humans and monsters, the enbodyment of hatred towards humanity itself, was taked along another amalgamates and locked up alongside them in the toxic wastelands (the hotlands version in ut:doomsday).

For years he was wandering the place, feeding up on radiation, until alphys tried to experiment with the amalgamates to find a cure to its horrible state, alphys discovered that using small dosis of dt can revert the effects of amalgamation, fusing the affected monsters and leaving behind one single body, alphys hesitated on curing crusher for a moment, but before she could do anything about it, he absorved the dt and broke free.

Because of the amount of monsters forming the amalgamate, crushers mind deteriorated, his body was formed around on what he hated the most, and is now wandering around the underground, until an interesting fellow made their apparition.