Percy the Small Engine is the No. 6 green engine on the Island of Sodor. He is the smallest and youngest member of the Sodor Railway. Percy was brought to Sodor by the Fat Controller when there was an engine strike due to a shortage of shunting engines. At first, the bigger engines tried to bully him, but Percy soon showed them that he is able to stand up for himself. Often seen happily puffing around the yard, Percy can be a little naïve and a bit overconfident, but he has little desire for wild adventures. Percy is Thomas' best friend and really likes to deliver the mail. He is very kind and always glad to help other engines, but they sometimes take advantage of his good nature.
The design of Percy is based on the 0-4-0 saddle tank engine from the Avonside Engine Company.