Culdee is a narrow gauge mountain-climbing engine who works on both the Culdee Fell Railway on Sodor and the Whitestone Mountain Railway. He has his own coach named Catherine.

Culdee is careful, cautious and friendly. He is filled with advice to give to the other engines, including unruly ones. Culdee is the sensible one of the Mountain Railway, and he often tries to tell difficult engines their faults and warns them what might happen. He and his coach, Catherine are a fine team, and favorites with passengers. But he does like a bit of excitement and tells great stories about the other engines.