Doc is a works tender engine who lives at Kahlville Works.
An old, experienced steamer, Doc is usually first to arrive at an emergency after the Crotoonian Rescue Squad/Patrol arrives. He'll usually examine the engine, and give them their diagnosis, along with assisting as much as he can. Doc is wise, experienced, and ready for any kind of emergency on the rails. He resides at the Kahville Works with Mary the Works Diesel, Kevin and Victor.
Doc is of a freelance design. He doesn't seem to be based on a specific prototype.
Doc is bright green with hazard stripes painted on the sides of his cab, a white medical cross painted on his boiler and a turquoise stethoscope on his front.