Oliver is a Great Western tank engine who was saved from scrap by Douglas. His daring escape made him popular with the other engines, which perhaps made him a little overconfident. He now works on the Little Western with Duck. He has two Great Western autocoaches, named Isabel and Dulcie and a brake van named Toad.

Despite his heroism and daring feats of escape, Oliver is an engine who is willing to admit every day is a learning curve. When he was still new to Sodor, he let the other engines' responses to his courage, resource and sagacity from his amazing recounts of daring escapes and adventures get to his smokebox and he became conceited. However, when the Troublesome Trucks pushed him into the turntable well, he grew into a much humbler, settled engine and was far warier of trucks. But later, with some help from his brake van Toad, he did gain much respect and authority among the trucks when he showed his strength with the ringleader of the trucks, S.C. Ruffey, a little more than he had perhaps been intending. Oliver still has gumption but is now a more obedient, sensible engine. He feels his responsibility on the railway deeply, is ever thankful for being aided in his escape from scrap by Douglas and is a trustworthy, tenacious, plucky engine. However, he can still be occasionally boastful or temperamental; despite this setback, Oliver is still one of the more really useful and well-behaved engines on Sodor.