Billy is a small orange tank engine with huge buck teeth. He is very stubborn and refuses to listen to advice, even when he does not know what to do.
When Billy first arrived on the North Western Railway, Thomas was given the task of showing him around. However, Billy mistook Thomas' words of advice as being bossy and refused to listen to him, neglecting to do almost all of his jobs and bumping Percy under the coal hopper. After many failed attempts to get Billy to listen to him, Thomas gave up and told Billy to do whatever he wanted to do, much to his delight. However, as soon as Billy was beginning to leave the yard, he ran out of coal and water, finally requiring Thomas' help. Once when Billy was refueled, Thomas helped him complete his jobs, and Billy finally admitted to him that he enjoyed working with him. (TVS; Don't be Silly, Billy)