Stanley is a silver saddletank engine. He works as both a shunting engine and a mixed traffic engine.
Stanley was brought to Sodor to take care of Thomas' workload during the restoration of Great Waterton. It had to be ready by Sodor Day. Upon his arrival, Stanley became very popular and enjoyed the company of the engines.
Stanley's popularity caused Thomas to feel jealous and later neglected. Thomas felt that Stanley was newer, bigger, and stronger than he - and would take over his place on the railway. Thomas then planned to make Stanley look weak - the trick backfired and caused Thomas' friends to consider him mean and incompetent.
When Thomas later went missing, Stanley was the first to realise Thomas' feelings. He searched for Thomas until he finally managed to find him in a ditch and rescue him. Then, both became friends and with a combined effort made it back to Great Waterton in time to prepare for the opening celebrations.
Stanley later worked in the yards with Thomas and James during the winter and helped with the rebuilding of the Sodor River Bridge. Also, he went to Great Waterton with Gordon to pick up passengers, and when Gordon bumps into a flatbed being pushed by Ben, he warns Stanley about the fallen logs and is able to warn him just in time.
Stanley was amongst the engines at Knapford who were worried about Percy's whereabouts when Percy was spending his time with the Diesels at the Dieselworks. Later on in the winter, he suffered from a faulty firebox and Thomas came to his aid once again.
More recently, Stanley can be seen working at the Shunting Yards, the China Clay Works and Ffarquhar Quarry. Salty also mentioned that Stanley, in one of his spooky stories, was an old engine who lost his flatbeds while climbing a hill, and ever since then his flatbeds have been stated to haunt the rails. When Samson backed onto Gordon's express coaches by accident when he was told to take stone to the Blue Mountain Quarry, Stanley tried to inform Samson that he had made a mistake, but the cabless tank engine refused to listen to Stanley, while proving not to make another mistake.
Stanley was also one of the engines told about the rumour of Toby being scrapped.
He also shunted a train of shiny branch line coaches for James one day, who was being his usual self; vain and overconfident, and when James was asked to take waste trucks to Whiff's Waste Dump, he questioned Stanley why he could not pull nice shiny coaches, in which Stanley tells James that Edward took them instead.
Stanley was also one of the many engines who wanted to go to the Great Railway Show. Like most engines, however, he was not chosen and was left on Sodor to do the other engines' jobs.
Stanley is the "boy-next-door" of Sir Topham Hatt's Railway. Cool, courteous, and cheery, he is a little bit bigger, a little bit newer, and a little bit stronger than Thomas, which, at first, made Thomas jealous when all focus seemed to be on this shiny, new arrival, especially when he began helping with the restoration of Great Waterton. However, even Thomas was soon won over by Stanley's positive attitude, charm, and friendliness and came to see why he was so popular and well-liked among the other engines. As such, Thomas and Stanley are now firm friends.
Stanley is incredibly compassionate and empathic: there is nothing he would not do for another engine. And if he could not do it, he would find someone who could. He is sleek, smart, and stylish, and his silver and light grey appearance, with striking red wheels and a shining smoke box certainly makes him look the part as he eagerly goes about his work.
Stanley is based on a hybrid cross of a Hudswell Clarke 0-6-0ST engine and Kitson's No. 5459 "Austin I", but with a taller funnel.
Stanley is painted in a silver grey livery with a metallic silver smoke box, red wheels and lining. He has a red running plate with a dark grey basecoat, and has red nameplates with his name in silver on each side of his saddletank.