Ren is smart in his own mind, but deep down he is a lot dumber than Stimpy. However, he often seems to be a hot-tempered, scrawny, mean, dyspeptic, very hyperactive, emotionally unstable, greedy, spoiled, and violently psychotic chihuahua. He has stated once in "Stimpy's Invention" that he "loves" being angry. He is extremely selfish and childish, and at tense times mentally unstable. He also is shown to have several mood swings. Cartoony, extremely loud, short-fused, violent.