Thomas was built in 1913 or 1915, and he arrived on Sodor in May of the same year. He was not supposed to work on Sodor, but a mix-up in Southern England led to him being sent to Sodor instead of his lazy brother 107, who was sent to the meat factory in Ireland where Thomas was supposed to be. Sir Topham Hatt chose to keep him because his brother refused to leave. He helped to build the North Western Railway. After the railway was built, he served as a station pilot who shunted coaches for engines like Edward, Eagle, Henry, and Gordon. He found the job very boring, and often wanted to see the world. In 1923/1945 (1925 in the RWS Universe), he did get two chances, for this, but they both went wrong. He left his coaches behind at the station while not realizing, and was pushed much too fast by some very Troublesome Trucks. However, in the same year, he was rewarded his own branch line after saving James from a nasty accident. He was also given his two coaches, Annie and Clarabel.
Thomas' first few years running his own branch line were quite eventful, and made new friends, a red bus named Bertie whom raced him, and a tractor named Terence, who rescued Thomas when he got caught in a snowdrift. When Percy arrived, Thomas and Edward began working the Main Line while Percy worked on Thomas' branch line. In 1951, Thomas got into trouble after he discovered that the line going from Ffarquhar to the Anopha Quarry only allowed engines with cowcatchers and side plates. Luckily, The Fat Controller was able to find a solution: Toby, a tram engine he had meet on his holiday. Toby arrived a few days later, and the two engines became close friends. When Thomas went off to the Toyreck Mines, he passed a danger sign out of curiosity, and fell into a mine. Gordon came to his rescue, much to the tank engine's dismay. After Sir Topham Hatt declared that he would take his engines to England after 7 BR Engines had come to work while he, Edward, Henry, Gordon, James, Percy, Toby and Duck went to England. The day before this was to happen, Thomas boasted to Jinty about his race with Bertie, only to crash into a set of buffers, but was repaired just in time.
In 1960, Thomas' driver mentioned that he had almost manage without him. This made Thomas conceited, and boasted about this to Percy and Toby. But his words got the better of him when he went off to breakfast at the Ffarquhar's Stationmaster's house the next morning. Donald and Douglas pulled him back to the yard and he was sent to Crovan's Gate to have his front end straightened. He didn't enjoy his time at the works. Thomas mentioned it was nice to be mended again, but they replaced so many of his old parts that he wasn't sure if he was him or another engine.
In 1990, Thomas was invited by the National Railway Museum to represent the North Western Railway in the Great Railway Show, an event showcasing many famous engines across the UK. Thomas was excited, but the journey to York was shaky; he damaged his front bufferbeam when he hit a crossing gate and the lorry he was travelling on was booked for parking illegally. Thomas was repaired when he arrived at the Museum and befriended Green Arrow while he was being mended, though he continued to have bad luck when he ran into a bag thrown onto the line and frightened a small child. Fortunately, Thomas managed to make up for his bad luck when, as he was double-heading a railtour with Green Arrow, he noticed the line up ahead was damaged and stopped the train. As a reward for his actions, Thomas was made an honorary member of the National Railway Museum and received a commemorative plaque. Afterwards, Thomas left York and returned to Sodor.
Thomas was also the one who found Neil.
Thomas is described as being a cheeky, fussy engine. He often gets into scrapes, usually by being over eager to do things best left to bigger and more sensible engines. But clouds never last long in Thomas' life and he is soon bustling about again, playing his part in the yard and on his very own branch line, of which he is extremely proud.
SI3D's 2010 model of Thomas was used in the first half of Season 1, "Haunted Henry", and the majority of "How the Diesel Stole Christmas". Then SI3D's 2012 "Christmas" model was used. The regular 2012 model made its debut in "Stuck!", and has been used ever since.
Thomas is based on LB&SCR Billington E2 Class tank engines. Ten members of This Class were built from June 1913 to October 1916. They were all withdrawn and scrapped from February 1961 to April 1963. What a shame.
- A Wretched Day for Henry and James (spoke in original script)
- Gordon Goes Swimming (part 1 only)
- Bill and Ben the Brave Brothers of Brendam (mentioned)
- Stuck! (cameo)
- Engine Unknown
- A Tale of a Small Green Engine
- The Runaway Railcar (does not speak)
- Attack of the Railway Pirates (credits cameo)
- Steaming Sausage
- Diesels and Dragons
- Painful Memories
- The Creature
- A Turning Point for Edward (cameo, appears in flashback)
- End of the Line for Edward
- Ivo Hugh's Safari (cameo)
- Highly Sprung (cameo)
- Gordon Pops In
- A Tale of Two Small Green Engines (cameo)
- Trouble in the 'Hood
- The Tale of Timothy
- Haunted Henry (part 1 only)
- How the Diesel Stole Christmas
- The Search for Smudger (cameo)
- Night Express to Vicarstown
- The Most Famous Engine (cameo)
- Revenge of the Ghost Train
- Tank Engine Mixup
- Two's Company
- The Trouble with Three
- Pride of the LNER
- Disgrace of the LNER
- Splendid Red
- Great Western Escape (cameo)
- Coach Trouble (cameo)
- Right on Traction (cameo)
- Double Teething Troubles
- Derek and Gordon (appears in flashback, cameo)
- Thomas1Edward2Henry3: Episode II-Haunted Henry, More Branch Line Engines-onwards
- JakerBraker123: NWR Origins, Specials
- RightonTracks10: How the Diesel Stole Christmas-A Tale of a Small Green Engine
Since Thomas is the main character of the show, he obviously appears in every season and special.
- When T1E2H3 voices him from Season 3 onwards, Thomas has a cockney London accent due to where his basis worked. It may also be a reference to Johnny Morris' Narration and/or JakerBraker123's Thomas voice.
- Despite being the main character of the real TV show, Thomas has had only three lead roles in The Engines of Sodor. In Engine Unknown (and even that is debatable as he never appeared until the second half of the episode but was the one who found Neil), Double Muddle, and The Tale of Timothy. This is so that the other engines can get a chance to do so, and the show doesn't just focus on him like the TV series does so.