- "Oh dear... This can't be good!"
- ―The Doctor, James Goes on a Trip
The Doctor is a medical doctor who works at Wellsworth Hospital.
When The Flying Scotsman was coming to Sodor, the doctor was one of the many guests gathered to see him arriving at the celebration.
Later, James' Fireman was ill and the doctor was called to treat him. However, he accidentally dropped his briefcase of medicines in James' open firebox, making the red engine take a "trip" of sorts.
He later came into the employ of the British Ministry of Defense and was stationed in their large outpost on Sodor during the "Munitions" fiasco. He treated General Zen after the latter was injured by flying debris, and notified the general that he had a surprise visitor.
After The Thin Controller's accident with Skarloey, the doctor treated the Controller's shattered femur. The Thin Controller explained how the accident had led to his wife finding out about his fencing lessons. The doctor reminded him that his fencing clearly had an effect on his health and safety, and warned him not to put to much weight on the broken leg. The Thin Controller thanked him and left for The Fat Controller's meeting.
After Culdee and Catherine successfully managed to bring back a wandering shepherd who had been holding onto Proteus' lamp and fallen off the bridge above Poll-ny-Chrink, the Doctor and two of his aides took the shepherd away to ask him a few questions.
- Season 2: Two Hearts Burn Together (cameo), Scot-free (cameo), Mavis and the Tornado (cameo), James Goes on a Trip, Munitions, All the World's a Stage (cameo), Swashbuckler
- Season 3: Culdee Fell, The Suggestion Box (cameo)