Culdee is an engine designed to climb steep mountains. He has a coach named Catherine which, contrary to most Coaches is pushed by Culdee rather than pulled. Culdee first met Percy in the shunting yards as he was on a flatbed. Culdee introduced himself and Percy was amused. Percy then asked if there were any diesels on his railway where Culdee replied saying that he had no idea what a diesel was and that there weren't any on his railway, Percy envied this as he thought that it was ideal. As the summer went on Culdee encountered Alfred Herman who was revealed to be Adolf Hitler himself and Culdee was then forced to take Hitler and his associated up the steep Culdee Fell mountain. Once on top Culdee was forced to have A missile attached to his train much to his displeasure. After coming down from the mountain the flatbed was transferred to the standard gauge line where duck proceeded to continue carrying the dangerous cargo. After the events of season 2 Culdee along with the other mountain engines have made various cameos throughout the series.
- Culdee is the only mountain engine as of now to have a speaking role.