- "He's so brave! I wish I could be like him- an example for the whole railway."
- ―Rosie talking about Thomas, Rosie (episode)
Thomas is a cheeky blue tank engine that works on his Branch Line with his two coaches, Annie and Clarabel.
Thomas was the station pilot at Vicarstown for eight years until he rescued James from a terrible accident. Since then, The Fat Controller has given him a branch line of his very own, where he now works happily with Toby, Percy, Daisy, Mavis, and occasionally Billy and Rosie.
Thomas rescued Daisy from a collapsing river bridge while Rosie looked on.
During one of his many 'specials', Thomas' path became intertwined with the dark events surrounding the Thin Controller. He first met Skarloey and Rheneas, before his train was mysteriously diverted to another track, preventing a hitman from shooting the Thin Controller. Mighty Mac blamed this on pigeons, and so Thomas' driver had them go slowly. Eventually though, Thomas grew impatient and picked up speed...causing him to slide onto slippery rails and into a fortune-teller's tent. The fortune told spoke of great change on the horizon, worrying the blue tank engine, particularly the part where he would be lost in the universe. He wondered if he had any control over it, or if he would do things just because he had to. This caused him to meet the Thin Controller once again, who consoled Thomas about this. Thomas would apparently take the man home numerous times afterward...
Much later, when BoCo and Arthur were discussing the mysterious markings of The Man in the Hills, they came across Thomas, who identified the figure as a legend Sir Handel had informed them of during The Thin Controller's birthday party, much to the surprise of the former two.
- Main Article: Everyone and Thomas
Thomas is a cheeky little tank engine with a long tongue, but he has proven his worth on multiple occasions. He does his best to help others and takes it upon himself to mend any sort of predicament. He is held in high regard, and even has his own branch line. He has been known to serve as a representative for all the engines on the North Western Railway on many occasions. Despite his cheekiness, he is a friend to all, and he is always willing to help a friend in need.
- Season 0: Snow Problem (does not speak)
- Season 1: Lift Bridge (cameo), Swagger and Swerves, Splatter, Dodge, Redemption (cameo), Bulldozer (cameo), Improvisation (mentioned), Snow Blind (mentioned), Scruff's Scaffolding (cameo)
- Season 2: Paxton and Norman, Serendipity (cameo), Rosie, Blunderbuss (cameo), Henry and Kurt, Swashbuckler (flashback cameo), Thomas and the Fortune Teller
- Season 3: Logan Leaves his Mark (cameo), Samson, BoCo, and the Man in the Hills, Culdee Fell (mentioned), The Suggestion Box (does not speak), Penn Pals (cameo), Ice Breaker (cameo), Percy and Asbestos
- Web Clips: Red Knight - Meet the Characters! (cameo), The Fat Controller, the Stationmaster, and the Raiboat - Meet the Characters! (cameo), Mike and Frank Banter: SLOTLT, ScarletFire, and EE93's Return (cameo), Thomas the Tank Engine 70th Anniversary Celebration! (does not speak), Thomas, Percy and the Blizzard of 2016 that was rather unnecessary and really came out of left field (does not speak), Gina gives Percy some pointers - Meet the Characters! (does not speak), Percy's Kafka Dream
- Thomas' 1992 model was used until EE93 started using the 2005 model in Blunderbuss. The "Sea Bound" model and "Surprised" Thomas models are also used to provide added expressions. His 2013 model was also used in Secrets of the Stolen Crown, with an added clay headlamp.
- Thomas was guest-voiced by ThomasWoodenRailway in Rosie.