Theodore is the youngest of the Chipmunks, usually singing upper harmony. He is shy, sweet, gullible, and naïve. In short, he is an easy target for Alvin's tricks. He wears green attire and has green eyes (brown in the CGI animated series). Theodore is often caught in the middle when Alvin and Simon get into an argument. He has a big appetite, constantly craving snacks and in one episode, Theodore tried to eat Alvin's hand because of his hunger. He plays the drums, the guitar, and other instruments. In vocal harmonies, his voice is typically the highest. He is fragile yet unpredictable and not very brave, but he will put on a brave face when his brothers are in trouble. At times, he is childish and Alvin's follower, but he is also the glue that binds his brothers despite Alvin and Simon's differences. Although he is sometimes teased by Alvin, Theodore loves his big brother and knows that Alvin loves him too.
He seems to have affection for Eleanor, who shares physical traits with him, but she is smarter, braver and more athletic. They each have a passion for the culinary arts, as Theodore is seen baking Christmas cookies in some Christmas episodes. In the live action/animated films, it is revealed that Theodore is sensitive about his weight and is often hurt when he is mocked for his chubby appearance. This also applies to Eleanor, but she is able to stand for herself and wishes that Theodore would do the same.
Like his brothers, he was originally voiced by Ross Bagdasarian Sr. In the animated series and film, his voice was provided by Janice Karman, Ross Bagdasarian Jr.'s wife and the voice of all three Chipettes. Jesse McCartney voiced Theodore in the live-action/animated film series.
