Peepi (also known as Ultra-Peepi) is a hamster in Invader Zim. Peepi was transformed into Ultra-Peepi when exposed to radiation, after Zim used a device to make him grow every time he ate. Peepi went out of control of Zim, and started destroying everything and killing everyone. Zim and the army tried to stop it, but for different reasons. The army wanted to stop it because it was destroying everything, and Zim wanted to stop it because it went out of his control. Zim stopped it by launching Peepi into space, but it crashed back down to Earth in an explosion.