Chaos is the name of a large alien monster, native to the planet Dredd. Its skin is composed of an unbelievably destructive mineral known as death crystals. Apparently, death crystals are also the only thing that can hurt it.
The Transformers cartoon
One hundred thousand years ago, Kup was visiting planet Dredd, when he was kidnapped by Orbs and forced to work in their death crystal mines. One day, Kup and the other slaves were attacked by some bat-like aliens, and a fellow slave explained that the aliens were fleeing from the monstrous Chaos. Seconds later, Chaos caused an earthquake that killed the entire group of slaves, except Kup, who ran off and found dozens of imprisoned robots in the caves. As he was preparing to free them, Chaos appeared, and Kup ran away in fear and left the slaves behind. Kup never forgave himself for this, and refused to recount this story to anyone until he discovered that the Decepticons had discovered the dangerous death crystals.
Returning to Dredd, where the Decepticons had constructed a giant death crystal cannon designed to destroy Cybertron, Kup reencountered Chaos in the caves. He yelled at the beast to go face a bigger monster waiting outside and ran off to rescue the robots and take them outside. When Chaos broke out of the caves, Kup and the slaves aimed and fired the Decepticons' cannon at it, obliterating the monster.