The Iron Warrior is really Prince Arin in a more agressive sense. In Episode 3: Guests of the Grunges, Grubby accidentally knocks Arin into a pot of Grunge Gumbo. He emerges as the Iron Warrior and starts to terrorize the Grunge Village. He gets in a fight with the Wooly What's-It and they fall off a cliff into a pool of water where Arin returns to his normal self, but with no idea of what had happened.
You'll notice some big differences in the transformation from Arin to the warrior (heavier armor, a larger and sharper sword, a mask over his helmet, and a change in his voice; not that he says much of anything). The Iron Warrior is very dangerous and just one example of how too much Vitamin Z in Grunge Gumbo can have a disasterous effect.
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