Stanley is a strong silver tank engine introduced in the movie The Great Discovery from Thomas the Tank Engine & Friends.
Stanley was brought to Sodor to take care of Thomas' workload during the restoration of Great Waterton. 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 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 is the "boy-next-door" of the Fat Controller's Railway. Cocky, cool, 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. There is nothing Stanley 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 smokebox certainly makes him look the part as he eagerly goes about his work.
Stanley is a based of hybrid mix of a Hudswell Clarke engine and Kitson's No. 5459 "Austin I".