Bertram used to work in the mines with the other "little engines" in a remote part of Sodor. His fate was unknown to many after the mine's closure, and it was assumed he was left to rust. He remained at the mine until it was rediscovered years later.
Over time, he became legendary; many knowing of the "old warrior ghost" haunting the mine. However, Toby found him whilst watching over the quarry one night, and has since befriended him. He now works at the restored mines, taking passengers to the fairground within.
Not much is known about Bertram's personality, however it is said that he is very brave.
Bertram is painted dark brown with red lining and has two brown plaques on either side of his saddletank with his name written in gold.
- According to Britt Allcroft, Bertram was supposed to be a tank engine, but financial difficulty in building a new model made them repaint Duke's model with Smudger's face. His Wooden Railway toy depicts him in his tank engine form.
- The ERTL model and TrackMaster prototype model have his name spelt as "Bertrum".
- The ERTL Bertram prototype had Duke's face.
- Bertram guest stars in The Skarloey Engines' Adventures of Pokemon: The Rise of Darkrai, The Skarloey Engines get Frozen, The Skarloey Engines' Adventures of King Kong,
- Bertram is best friends with Shady Daze.