Duke is a brown narrow gauge engine.
Duke was built at Boston Lodge in Minfford, Wales in 1879 before being transported to Sodor for the opening of the Mid Sodor Railway in 1880.
In 1947, the line closed and Duke was sheeted and sheltered in Arlesdale Sheds. He was later discovered by Fergus Duncan, the Reverend Teddy Boston and the Reverend W. Awdry in 1969 and taken by road and rail to Crovan's Gate, where he was restored and returned to service in 1982/3.
Duke is one of the oldest and most experienced engines of the Narrow Gauge Railway. He is also the mentor of Peter Sam and Sir Handel, from their older days on the Mid-Sodor Railway, when they were called Stuart and Falcon respectively. Although once lost for many years in an old shed that nature tucked away and forgot, after the Mid-Sodor Railway came to an end, he was found by rescuers, although quite by accident, when one came in through his shed roof. He may have a head teacher attitude and maintain his authority at all times, but can be quick to apply his knowledge and years of experience to help guide and correct any younger engine. He is proud of his name and keen to uphold the respect it merits. He can often be heard to say "That would never suit his Grace!" upon hearing or seeing something that he takes a disapproval to, or pedantically stating how he thinks someone would have adhered to the rules and regulations in his young days. Despite their teasing ways, Sir Handel and Peter Sam in particular have grown to become very fond of Duke and dearly nicknamed him "Granpuff".
Duke is painted brown with yellow lining and has two red plaques on either side of his saddletank with his name written in gold.
- Season 1 - Harvey Goes Fishing (cameo), Sir Handel and the Ghost Engine, The Old Warrior, and Butch's Chase (mentioned)
- Season 2 - Rheneas and the Dinosaur, Hiro and the Express, Paul and Rusty, and The Importance of Being Neville
- Season 3 - The Fastest Engine in the Hills, Skarloey and the Mountain Bikers (cameo), Don't Be Late!, and Luke and the Christmas Party
- Season 4 - Duke's New Grace and Harold and the Climbers (cameo)
- Season 5 - Culdee and the Enthusiasts (cameo), Stanley's Branch Line (cameo), High Expectations, and Creepy Cutting
Shorts: The Legend of the Gold Train
The Adventures on Sodor
- Season 1 - Old and Wise, Dashing Duncan, Sir Handel and the Coal Mines, Skarloey Comes Home, Rheneas' Risky Ride (cameo), and Rusty Rescue (cameo)
- Season 2 - Trouble on the Line, Duncan's Discovery, and The "Ghost" Warrior
The Many Adventures on the Island of Sodor
- Season 1 - Old Engine, New Changes and Duke Does it Again
- Season 2 - Arthur's New Route (cameo), Second Rate Engines (cameo), Peter Sam and the Lost Engine, and The Search for Neil
Adventures on Rails