Theodore is the child of innocence and the youngest. He is shy, loving, good-hearted, sensitive, chubby, gullible, trusting, and naïve. In short, he is an easy target for Alvin's manipulations, he wears green and has green eyes. Theodore often holds the swing vote between his two brothers' choices of action. Simon appeals to Theodore's better nature while Alvin goes straight to bribery. He is constantly craving snacks.

He is fragile yet unpredictable, you never know when he'll take a bit out of the nearest flesh. At times, he is childish and Alvin's follower. He is the glue that binds his brothers despite Alvin and Simon's differences and regular disagreements.