Duke is an old narrow gauge engine, who used to work on the Mid Sodor railway.
Long ago, Duke worked on the Mid-Sodor Railway with Sir Handel (known as Falcon), Peter Sam (known as Stuart), and Smudger. Sometimes they doubted Duke because of his age, but he always proved his worth. He rescued Falcon from almost rolling down a mountain, showed Stuart that he had the strength to carry the train home even when he had broken down, and tried to keep Smudger out of trouble. They worked happily together for many years until their line was closed down. Stuart and Falcon were sold to another railway, and Duke was left alone in the shed. Many years later, a rescue party was brought together to find him, and with a great deal of determination, they succeeded! The team brought Duke to his new home, the Skarloey line, where he was joyfully reunited with Stuart and Falcon. Smudger had been turned into a generator, and would never be able to join them.