He is one of the two harbour tugs along with Hank, moving barges and being pushers during ship docking operations. In the books by Michelle Mulder, Theodore is seen with another harbour tug named Lucy.
He is kind, but sometimes cheeky and fussy. He will help any tug in need. His goal is to be an ocean tug and to travel to other harbours across the world. But before that he must master the job of a harbour tug. He always tries to be friends with everyone who visits the Big Harbour.
According to Andrew Cochran, to build Theodore Too, he was planning to modify a tugboat that looks like Theodore. It was to be used for marketing and promoting water safety. Eventually after all the hard research, none were close enough just to modify as Theodore. As a decision, Andrew Cochran has decided to build a Theodore from scratch design by model maker of the show Fred Allen. So thus it has come to being that Theodore is of a fictional design.