Thomas is a cheeky blue tank engine who works on the North Western Railway. He originally worked as the station pilot at the Big Station, but longed to leave his yard to go out and see the world. After helping to rescue James from a nasty accident, Thomas was rewarded with two new coaches, Annie and Clarabel and was given the responsibility of running the Ffarquhar Branch Line, where he continues to work to this day.
Thomas is a cheeky, fussy little engine who very often ends up getting into a scrape or two! A hard working, but sometimes mischievous friend, he runs a branch line on his home (the Island of Sodor) and helps run another on Crotoonia, which travels from Celgreb City to Inkblotia Castle! Even though he may seem like a really cheeky and fussy engine, he's a kind and positive-thinking friend who always tries to put things right.
Thomas is based on an LBSCR E2 Class, more specifically the version with the extended side tanks, these tank engines were built at Brighton Works between 1913-1916 to replace the E1 Class.
They were used for shunting duties and short-distance goods trains in London and on the south coast, and last worked at Southampton Docks. None were preserved.
However in Crotoonia, a replica of his class works at Pinewood Island.
- Thomas was the first character in the Railway Series to have a number. According to Brian Sibley, Awdry used the number one because it was the easiest to draw.
- Thomas was the first character introduced in the television series.
- Christopher Awdry lost the original Thomas toy when he was in the United States. However, it was recreated in 2015 for a 70th anniversary sizzle.
- Thomas' LBSC number, 70, was actually carried by a real LB&SCR locomotive, an A1 named "Poplar" currently preserved by the Kent & East Sussex Railway. The number also represents the 70th anniversary of the Railway Series.
- According to Sir Topham Hatt on the 2001 Official Website, Thomas was given his name by the engine workshop which built him.
- Thomas is one of the few characters to appear and speak in every season and special.
- A Wooden Railway toy of Thomas along with one of Stepney's appeared in the second season of the Big Bang Theory in the thirteenth episode, The Friendship Algorithm.
- An ERTL toy of Thomas along with one of James' also appeared in the sixth season of Full House in the fifteenth episode, Be True to Your Preschool.
- Thomas has undertaken the most changes since the series entered production, due to constant updates to his model; currently, the series uses Version 8.