Percy is small green saddle tank engine that works shunting freight on the branch lines and in the yards.
Percy was brought to the railway when Gordon, Henry, and James refused to shunt their own coaches. After a traumatic experience with Gordon the big engine nearly hitting him with the Express, The Fat Controller thought it best to send the cheerful green tank engine to work elsewhere. He now works happily on Thomas' branch line, and is also a resourceful "odd jobs" engine capable of many other duties all across the board.
Leaving the milk behind on purpose for the umpteenth time, Percy was fed up with Daisy's rampant swagger. However, Daisy's accident later that afternoon certainly cleaned up her act! After that fiasco, Percy rarely has to take care of the milk run for the sassy diesel rail-car.
The little green engine was a target for Norman and, against his will, Paxton, to prevent Norman from being sent away from Sodor. The plan, however, did not take off. Percy inadvertently took Paxton's sabotaged truck, which eventually lead to Paxton almost being blown to smithereens in a mine shaft.
The trucks, in recent days, have been tiring Percy out. Percy has occasionally taken out his frustration on his friends, but quickly was reminded on what karma can do to an engine!
When strange footprints were discovered at the China Clay Works, Percy became nervous about what they could mean. This fear strained his friendships with Thomas and James, with the former being unsure if the footprints were real, while the latter engaged in a series of escalating pranks to scare Percy. Thankfully, Percy made it through the ordeal thanks to the teachings of Gator, who taught him how to face his fears. It ultimately culminated in Percy rescuing James from a landslide at the Clay Pits, which in turn revealed that the footprints were fossils of a dinosaur!
Percy was later approached by Rosie to help Culdee recover mentally from the latter's traumatic accident. He did so by utilizing Gator's teachings (And funnily enough, Culdee had actually talked with Gator about facing your fears just before he had had his accident) and relaying his own experiences with fear, which successfully pulled Culdee out of his funk, upon which the mountain engines left to complete his assignment of rescuing a shepherd dangling from a bridge.
Percy acted as an intermediary between Hank and Philip when the Philip wishes to apologize for his misstep but is unable to leave the yards. Accordingly, Philip sends his apology via letter to Hank at the Works on Percy's mail train.
Percy can be a bit cheeky, silly, naive, grumpy, and mischievous, but he is still a good friend to all the engines on the North Western Railway. An optimist, Percy always puts a smile on everyone's face. The one job Percy loves the most is taking the post train around Sodor.
As of recently however, Percy has started to become far more cynical and tempered. Due to the Fat Controller giving him more and more work to do, Percy often feels put upon with work. Sometimes, this anxiety causes him to lash out at his friends. He loves playing jokes occasionally, which can land him into a lot of trouble. Despite everything, he is still a fiesty little saddle tank with a big heart.
As he gained more experience, his signature cheekiness, by his own accord, slowly disappeared as the world itself seemed larger and more menacing. Percy thus has developed a fear of the unknown, but thanks to his experiences with Gator, he has learned that while that our fears will never go away, we will always face them, not worrying when there is no need to.
- Season 0: Snow Problem (does not speak), Cab Over Wheels (mentioned)
- Season 1: Lift Bridge (cameo), Swagger and Swerves, Splatter (cameo), Dodge, The Old Warrior, Bon Voyage, Bulldozer (cameo), Shepherd's Pie (cameo), Conspiracy Theory (cameo)
- Season 2: Paxton and Norman, Serendipity (cameo), Scot-free, Mavis and the Tornado (cameo), Rosie, James Goes on a Trip (does not speak), Rock-Star, Pummeling Percy, Munitions (cameo), Aura of Menace (cameo), Swashbuckler (flashback cameo), Thomas and the Fortune Teller
- Season 3: This Too Shall Pass (cameo), Logan Leaves his Mark (does not speak), Culdee Fell, Derek and the Two Faced Engines (mentioned), Penn Pals, Ice Breaker (cameo), Percy and Asbestos, Stafford's Request (cameo), Carols in The Forest
- Web Clips: The Fat Controller, the Stationmaster, and the Raiboat - Meet the Characters! (cameo), Thomas the Tank Engine 70th Anniversary Celebration! (cameo), Thomas, Percy and the Blizzard of 2016 that was rather unnecessary and really came out of left field (does not speak), Gina gives Percy some pointers - Meet the Characters!, Percy's Kafka Dream
- Percy's 1999 model is the one used regularly. However, his 2011 "Oil-Covered" model, his 2010 Snowplow model, and his 2006 "Hard at Work" model have been used in Season 3 to depict a greater variety of expressions. His "Jack Frost" model was used in the custom model spotlight of the troublesome goods van and narrow gauge coaches. His 2002 model was used from Snow Problem onwards.