Don Onion is the main antagonist of the video-game "The Munchables" and is the highest-ranking leader of the Tabemon Monsters.
Long ago Don Onion and the Great Elder were the best of friends and worked together for the benefit of the world, researching ways to create good and healthy Tabemon Monsters.
However things changed for the worse when Great Elder stumbled upon Don Onion's horrific secret, he was transforming regular Tabemon Monsters into horrible mutated monsters via insane experimentation.
Enraged at the defilement of the creatures he'd been caring for the Great Elder confronted Don Onion only to be knocked aside as Don-Onion became insane and vowed to conquer the entire universe using his new creations.
The Great Elder left in utter disgust at his former friend's madness and years later would come to regret not having stopped him as Don Onion returned with many Tabemon Monsters to make good on his promise to take over the universe with the aid of the Legendary Orbs.
Don Onion is confrontated for the first time by the Great Elder and the hero after they fight their way to Mount Brim and he unleashes his most powerful minion, Rice Baller, to dispose of them.
However after the defeat of Rice Baller Don Onion flees the scene and later feigns friendship with his former enemies by sending a letter saying he was sorry for his misdeeds and inviting them to a party.
The Great Elder (somewhat foolishly) believes Don Onion's lie and goes to the party alongside the hero, which is hosted at Don Onion's own space ship.
However Don Onion is quick to turn on the two and traps them in the space ship, revealing his masterplan to fuse his Pumpkin Ship with the Legendary Orbs to form a doomsday weapon by which to conquer the universe.
In order to escape the space ship the hero must defeat all the previous Boss Pirates he had defeated (though they are slightly more powerful and most likely clones, since the original Boss Pirates were devoured by the hero previously).
Once they escape the Great Elder and the hero face off against Don Onion in the final boss fight of the game where he battles the hero from within the giant robot known as King Pumpkin.
Using the powers of the Legendary Orbs and yhe King Pumpkin armor Don Onion is a formidable opponent but is ultimately defeated in a climatic battle.
Miracolously Don Onion survives the fight and manages to sneak off using a rocket while the game's two heroes are distracted (namely by trying to eat the Great Elder - a running joke in the game).
However Don Onion's escape is foiled as he underestimated the ability for the hungry heroes to sniff out food and they soon devoured his getaway vehicle, causing it to crash back down to earth.
It is unknown whether or not Don Onion survived or if he was spared the fate of his fellow Boss Pirates (he may of survived, considering the two heroes often attempted to eat the Great Elder but never actually did so (and Don Onion appears to be the same species as the Elder).