Smudger worked on the Mid Sodor Railway with Duke, Sir Handel, and Peter Sam. He rode roughly and often caused confusion and delay. Duke warned him but he never listened. One day he had to pull a passenger train with Duke through the mountains. Smudger rode roughly again, but instead of just derailing like normal, he fell down the mountain with the train. The railway's controller was furious with Smudger and turned him into a generator as a punishment. Smudger sat behind the shed and was left there after the railway closed. He sat for years and years, eventually losing his mind and wishing for death.
Duke told the narrow gauge engines the story of Smudger and how he fell off of the mountain. They were horrified. Later, the Thin Controller and some friends went to the ruins of the Mid Sodor Railway to find Smudger, as they needed another engine. Smudger wished for them to kill him and he screamed and shouted, but the Thin Controller calmed him down and eventually convinced him to work for him. Butch towed him out of the ruins and to the Sodor Steamworks. There, Smudger was rebuilt back into his engine form. A few days later, he arrived on the Skarloey Railway and came face to face with Duke.
Smudger used to be young and arrogant. He rode roughly and was very disrespectful. After he was turned into a generator though, things changed. Smudger deteriorated inside and out and went insane over the course of many many years. He was suicidal and wished for death, but eventually the Thin Controller found him and had him changed back into an engine. Smudger now will have to be reintegrated into society, and it won't be easy.
- Smudger is the first character to have an episode named after him