Theodore is the main protagonist of the series same name. He is one of the smaller tugs and wears a red baseball cap. He is a harbour tug, like his best friend, Hank.
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.
Theodore is kind, but he can have a tendency to be 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.
Theodore is loosely based on a Turecamo Girls tugboat modified into a freelance design.
He plays Snowbell in Thomas Little (Stuart Little) (Daniel Pineda's Style), Thomas Little 2 (Stuart Little 2) (Daniel Pineda's Style) and Thomas Little 3 (Stuart Little 3) (Daniel Pineda's Style)
He is a cat.
- Season 1 - Theodore and the Oil Rig, Theodore and the Homesick Rowboat, The Dark and Scary Cove, Foduck the Vigilant, Different Strokes - Different Boats, Hank and the Mermaid, True Blue Friends, Bumper Buddies, Theodore and the Welcome, Theodore the Vegetable, The Day Ice Came to the Harbour, Theodore's Bad Dreams, Theodore's First Pull, Theodore and the Queen, Theodore and Bluenose, Is Anybody Listening?, George Buzzes the Dock, The Big Harbour Clean Up Contest, Best Friends, and Theodore and the Big Harbour
- Season 2 - Theodore's Whistle, George's Ghost, Theodore Changes Sides, Night Shift, Whale of a Tug, The Tugboat Pledge, Emergency, The Cold Snap, Hank and the Hug, Emily and the Rocket, Foduck Stays Home, Theodore the Tug in Charge, Theodore in the Middle, Carla the Cool Cabin Cruiser, Snorri the Viking Ship, Tug of the Year, Theodore the Jokester, Emily the Vigorous, Theodore's Day Off, and Foduck and the Rainbow
- Season 3 - All Quiet in the Big Harbor, Theodore to the Rescue, A Joke Too Far, Theodore and the Ice Ship, Big Harbor Fools Day, Grumpy Garbage Barge, Theodore Hugs the Coast, Hank's Hiccups, Hank's New Name, Theodore and the Northern Lights, Big Harbor Birthday, Theodore's Backwards Day, Scally's Stuff, Theodore's Big Friend, Theodore and the Missing Barge, Theodore and the Borrowed Bell, Emily's Close Call, Emily's New Hat, Emily and the Tug-Of-War, Theodore and the Lost Bell Buoy, Theodore and the Bully, George and the Underwater Mystery, R. Boat and the Queen, Hank and the Night Light, and Theodore and the Pirate
- Season 4 - Foduck's Hurt Feelings, Theodore's Tough Tugging, Theodore's Ocean Adventure, Theodore's New Job, Digby's Disaster, Dartmouth Says Goodbye, George's Funny Noise, Rebecca's Treasure, Guysborough's Garbage, Theodore's Visit to Ceilidh's Cove, George's Turn, Theodore Lands On Earth, Hank Makes A Friend, Foduck Blows His Stack, Sigrid and the Bumpers, Hank's Wheezy Whistle, Theodore and the Haunted Houseboat, Northumberland is Missing, Emily Goes Overboard, Emily and the Splash, Rebecca and the Big Snore, Theodore and the Lies, Theodore's Bright Idea, George and the Navy Ship, Theodore's Prize, The Dispatcher's Best Birthday, Emily's Easy Job, Nautilus and the Sinking Ship, Owan On the Loose, and Emily's Bruised Bumper
- Season 5 - Theodore Shares his Story, Hank Hurts a Ship, Theodore and the Harbour Crane, Theodore On Time, George's Big Hurry, Theodore and the Buoy Boat, Theodore Gets Lost, Hank's Funny Feeling, Theodore and the Runaway Ferry, Theodore and the Scared Ship, Foduck in Reverse, Hank and the Sunken Ship, Theodore and the Bickering Barges, Theodore the All-Powerful, George and the Flags, Hank Stays Up Late, Theodore the Tattletug, Brunswick's Big Scare, Hank and the Silly Faces, Emily Finds A Friend, Hank's Cozy Cove, Theodore and the Hunt for Northumberland, Bedford's Big Move, Emily Drifts Off, Guysborough Makes a Friend, Theodore and the Missing Siren, Pugwash is Gone!, Theodore and the Unsafe Ship, Emily and the Sleep-Over, Foduck and the Shy Ship, Theodore Takes Charge, Theodore's Bright Night, George Waits His Turn, Hank Floats Forward, and Theodore's Big Decision
- He also appeared in all of the books that was published when the series was still airing. He also appeared in four books that was written by Michelle Mulder under the name Theodore Too.
- Theodore Too's base model was sold on ebay.
- Theodore's television series model is currently on display at the Maritime Museum of the Atlantic.
- Theodore's whistle can be heard in several episodes of Thomas the Tank Engine and Friends at Brendam Docks since the CGI switch.
- Theodore's whistle can be heard at the end of the Mayday episode, "Collision Course: Sinking of the Express Samina".
- In the Swedish version, Theodore is called Bosse.