Percy ran Thomas' branch line while Thomas ran the mainline with Edward, and was allowed to stay after the big engines surrendered. At first, Percy liked to annoy the big engines. Percy was later waiting at Tidmouth but forgot to whistle to the signalman, and thus was startled when Gordon came running towards him with the Express. Gordon managed to stop in time, but Percy was frightened, ran away, and ended up in a sandbank. He was rescued by Gordon, and took up the duty of station pilot at Tidmouth.
Percy was still a cheeky engine and often liked to play jokes on Gordon and James, but one day the other engines got their revenge when Percy failed to recognise a "backing signal". After this, Percy was subject to bullying from the big engines until Duck arrived and helped Percy to put the big engines in their place. With Duck's arrival, Percy was sent to Knapford to help build the harbour, and has stayed there ever since as a goods engine.
Percy is a cheeky tank engine, and Thomas' best friend. He is fun-loving and enjoys playing jokes, which can sometimes get him into trouble.
Percy is kind hearted and cares a lot about the other engines - male or female - and will help them when they need him.
Percy has been dumbed down in order to teach viewers difficult words: he would say "dingy-fried" where anyone else would say "dignified". He also is shown to make obvious mistakes. Although slightly naive and easily scared, Percy wants to prove to be a really useful engine.
Percy is incredibly accident-prone, and holds the dubious record of the most accidents in one season - 5, in the 2nd season - crashing into some buffers, falling into the sea, being pushed onto a brake van, colliding with a cart and being hit by a falling crate of treacle. So far, his silliest accident yet was in the 6th season, when he slipped on oily rails, crashed through the chocolate factory and emerged covered in chocolate.
Percy is primarily based on an GWR Avonside 0-4-0ST with the body of a GWR 1340 Trojan (who is now preserved at the Dicot Railway Centre), the bunker of a GWR 1361, Hunslet under frames and valve gear, a smoke box protruding from his saddle tank, external cylinders and motion and sandboxes underneath the tanks on the footplate, approx. 20ft 1in long. First, his whistle valve has a triangular cone base, and a cylinder-shaped top like Gordon's whistle. Afterwards, the base is rounded, but the top is still flat. Finally, the top and base are both rounded. He also has the maximum speed of 25 mph.
Modifications made to Percy's shape are needed the angled smoke box supports and the cab being cut down slightly from the back for the bunker.
Percy is painted NWR green with red stripes on his boiler and cylinder box, a small brass dome and a "6" painted on his cab sides in yellow with red border.
The Reverend W. Awdry and C. Reginald Dalby did not get along very well. Awdry considered Dalby's drawings "toy like"; this relationship was worsened by the creation of Percy, who was depicted as an Avonside 0-4-0ST/GWR 1340 Trojan with a bunker.
When Percy the Small Engine was published, Awdry wrote to Dalby criticizing his illustrations and claiming Percy resembled "a green caterpillar with red stripes". This was too much for Dalby, and he promptly resigned. However, the insult was not forgotten: Thomas called Percy "a green caterpillar with red stripes" in "Tramway Engines".
- Michael Angelis (Thomas and the Magic Railroad original workprints only)
- Linda Ballantyne (Thomas and the Magic Railroad)
- Keith Wickham (UK; Hero of the Rails - Sodor's Legend of the Lost Treasure)
- Nigel Pilkington (UK; Series 19 onwards)
- Martin Sherman (US; Hero of the Rails - Season 18)
- Christopher Ragland (US; Sodor's Legend of the Lost Treasure onwards)
- Marina Huerta (Mexico; Series 1 - 4)
- Enrique Cervantes (Mexico; Series 5 - 7)
- Edson Matus (Mexico; Series 8 onwards)
- In the French version of Thomas and Friends, Percy is called Pierre.
- Percy's whistle sounds like 2 high pitched blasts, higher than Edward's.