Percy is the No. 6 green engine. He is the junior member of Sir Topham Hatt's railway. He is quite content puffing around the yard with no particular desire for adventure in the world outside. Percy is Thomas' best friend and his favorite job is delivering the mail. He is always happy to help and other engines sometimes take advantage of his good nature.
- Percy is an 0-4-0 saddle tank engine based on engines from the Avonside Engine Company.