Den is a big diesel-hydraulic engine who runs the Vicarstown Dieselworks with his assistant, Dart.
Thomas & Friends
In Day of the Diesels, Den and Dart took Thomas to the back shed of the Dieselworks while Percy, Diesel 10 and the other diesels took over the Steamworks.
In the fifteenth season, he, along with Dart and Diesel, tried to find a Christmas tree for the Dieselworks whilst in competition with Thomas. Den later teased Flynn for spraying the Fat Controller and Gordon.
In the sixteenth season, he helped Thomas fix Ol' Wheezy and repaired Gordon's bufferbeam.
In the seventeenth season, Den, with Dart, help fixed a sputter in Salty's engine.
In the eighteenth season, Den, along with Dart, Sidney, and Diesel hid from Paxton, causing Paxton to search for them.
In the nineteenth season, he was sent to the quarry as a replacement for Mavis while she was at the Dieselworks. Initially, Den struggled with the troublesome trucks, but after some encouragement from Toby and Henrietta, he toughened up and finished his job. When Mavis came back, Den went back to the Dieselworks.
In The Great Race, Den, along with Dart and Paxton, was part of Diesel's plot to be taken to The Great Railway Show. Diesel had the three put under crates in a large train, making them resemble vans. When the Fat Controller was in the final stages of choosing who would go to the show, Diesel would then honk his horn to signal the three to start pushing, making it look as if Diesel was moving the train by himself, whereas the other three diesels would actually be doing most of the work, which Diesel hoped would convince the Fat Controller to take him to the show. The day before the show, Diesel refused to move his train from blocking all ways in and out of the yard, leading Thomas, who was in a hurry to demonstrate his shunting skills to convince the Fat Controller to enter him in the shunting competition, to move Diesel's train himself. When he whistled after a shunter coupled him up, the diesels mistook the tank engine's whistle as Diesel's horn and started pushing the train as they were instructed to. Thomas was surprised at the train pushing him and Diesel was horrified, thinking Thomas was pulling the train, realising his chance would be ruined. Though Sir Topham Hatt was impressed with the heavy train Thomas was "pulling," Thomas then collided with Norman at a set of points, losing his left buffer and ruining his chance to enter the show as well. Later, Diesel confronted the three and nearly forced Dart off the Dieselworks turntable, but instead made Dart bump into a button, sending a crate down on Diesel. Diesel later escaped to Brendam Docks, and the three continued to hunt him down, only for Cranky to load him onto a ship bound for the mainland.
Den is the diesel engine who runs the Vicarstown Dieselworks, repairing other diesels. He is stately and deeply pensive. He tries to make sure everything he says is deeply considered, can often be heard muttering "what I mean to say is...", and can tend to over-think. He may come across as a little slow, but nothing could be further from the true. He is rather astute and likes to take into account much as he can with regards to a problem. Although he is not a worrier, he may tend to be on the fence about taking particular action over a matter before making a calculated, informed decision that will be worth the wait. Sometimes though, Dart, his assistant at the Dieselworks, can tell what he is thinking and cut to the chase a little quicker for the benefit of the other engines, which is why they support each other so well as a team. Den is a hard worker and is popular and well respected among the diesels for fixing them with a whisk of his wheels, even if his tools may be old and shoddy and his machinery may be outdated. Although he is trustworthy and authoritative, Den may have the occasional chuckle at an engine's expense.
Den is based on a Rolls Royce Class 4DH Sentinel diesel-hydraulic 0-4-0. These engines were bult to replace Sentinel's steam line for usein various industrial shunting roles. Larger 0-6-0 and 0-8-0 variants were also produced. Several engines of this type are preserved, including one at the National Railway Museum, and another at the Bluebell Railway.
Den is painted slate grey and orange with cream lining. His buffer beams are painted with orange and black wasp stripes. He has the Vicarstown Dieselworks logo on each side of his cab.
Thomas & Friends
- Series 15 - Stop That Bus! (cameo), Stuck on You (cameo), Tree Trouble and Fiery Flynn
- Series 16 - Ol' Wheezy Wobbles, Thomas Toots the Crows and Bust My Buffers!
- Series 17 - Away From the Sea
- Series 18 - Disappearing Diesels
- Series 19 - Den and Dart
- Series 21 - Springtime for Diesel, Dowager Hatt's Busy Day (cameo), Daisy's Perfect Christmas and The Big Freeze
- Series 22 - Hunt the Truck (life lesson; cameo) and Counting on Nia (life lesson; cameo)
- Series 23 - Diesel Do Right, Steam Team to the Rescue and Diesel Glows Away
He may appear in the twenty-fourth series.
- 2011 - Day of the Diesels
- 2016 - The Great Race
- 2017 - Journey Beyond Sodor (cameo)
- Day of the Diesels - Day of the Diesels
- Series 17 - On a Journey Today
- Thomas' YouTube World Tour - Navigation
- Series 19 - Engine Roll Call
- The Great Race - I'm Full of Surprises
- Journey Beyond Sodor - I Want to Go Home (cameo)
- Series 21 - Set Friendship in Motion and Trying
- Series 22 - Engine Roll Call
- Welcome to the Island of Sodor Logan! (does not speak)
- A Friendly Farewell (cameo)
- 2012 - Ol' Wheezy Wobbles and Thomas Toots the Crows (does not speak)
- 2014 - Salty's New Friend (does not speak), Wobbly Ol' Wheezy, and Leaves on the Line! (does not speak)
- 2015 - Bust My Buffers! (mentioned)
- 2016 - Thomas Toots the Crows
- 2017 - Den and Dart
- Keith Wickham (UK/US; Day of the Diesels onwards, excluding Fiery Flynn)
- Rupert Degas (UK/US; Fiery Flynn only)
- Ryuzou Ishino (Japan)
- Fredik Paasche (Norway; Day of the Diesels only)
- Sigbjorn Solheim (Norway; fifteenth - seventeenth series)
- TBA (Norway; eighteenth series onwards)
- Burkhard Schmeer (Germany)
- Piotr Bak (Poland)
- Dan Schatzberg (Israel)
- Victor Covarrubias (Latin America; Day of the Diesels onwards)
- Bernard Demory (France and French speaking Canada)
- Tiaggo Zambrano (Brazil)
- Angel Amoros (Spain)
- TBA (Russia; Day of the Diesels - eighteenth series)
- Denis Bespalyy (Russia; nineteenth series onwards)
- Jukka Voutilainen (Finland; Day of the Diesels onwards)
- Haris Grigoropoulos (Greece)
- In the nineteenth season, Den gained a standard tail lamp, despite already having two the same design as his front lamps.
- Wooden Railway (discontinued)
- Take-n-Play (normal and talking; discontinued)
- Adventures (sold only in Dieselworks Fix-Up 4-Pack; discontinued)
- Mega Bloks (discontinued)
- Wind-up (Japan only)
- Pocket Fantasy (discontinued)
- Capsule Collection