He is a big flying tomato, who can trap others in pickles and turn ripe produce rotten.
Rotten Tomato is the villain from the story in The Grumpfish Special! , titled Super-Waiter and Busboy. He is a giant red tomato who aims to make sure Super-Waiter and Busboy don't get the order to the customer. When the two heroes reach the Garden of Doom to pick vegetables, he turns Super-Waiter into a pickle. He is then defeated at the end of the story by being trapped in a ketchup bottle by Busboy.
He reappears in Fruit Camp! as a villain who wants to turn all the produce rotten. At the end of the story, he tastes how delicious ripe produce is and vows to never make produce rotten.