Percy is a rather cheeky, but kind engine, and generally behaves well, except when he is getting into mishaps from being over-eager. He loves teasing the others, especially the bigger engines, such as Gordon and James, but is always brought down to earth in due course by anyone who gives him the moral to learn, especially the Fat Controller.

During WWII, Percy is put into a group with Henry and James and all three are shipped to Africa. Whilst there, Percy is put by foreign engines for his size, but he proves his worth when he assists in rescuing an LMS 8F with Henry. He speaks with a cockney accent.