Bert is a blue miniature tender engine who works on the Arlesdale Railway engines. He is one of the quietest engines, but is not afraid to get back at someone he thinks has wronged him.
The Railway Series
Before he came to Sodor, Bert used to work on an unnamed miniature railway in England alongside Rex and Mike, but their railway was closed. Following the closure of their previous line, the Fat Controller brought them to Sodor to work on the Arlesdale Railway.
When the Fat and Thin Clergymen came to the Arlesdale Railway to photograph the line for a new book, Bert initially thought that he would be physically placed inside the book and remained apprehensive until he met them, after which he cheered up. However, Bert became annoyed when they did not wave to him, and became infuriated when they splashed him with muddy water. Bert planned revenge, and when the Fat Clergyman rode in his tender on the way back, Bert soaked him and his driver. Bert was punished for this and apologized to the two clergymen, who accepted his apology. (RWS; Small Railway Engines)
Bert began having trouble with steaming properly, as he was having difficulties with his tubes, though Rex and Mike were both unsympathetic. One day, as he was preparing to leave the top station with a passenger train, his coupling broke. His driver used glue to secure the coupling hook, and Bert managed to bring his train home in time. Bert was also the first one to find out about Jock being built. (RWS; Jock the New Engine) Bert later recalled this incident to Wilbert when he experienced a similar problem. (RWS; Wilbert the Forest Engine)
Bert continued to have trouble steaming properly, but this problem was cured when he was overhauled in 1973, receiving a taller funnel and cab and giving him a narrow gauge outline appearance.
When the Harwick Branch Line was under construction, Bert and the other two small engines were given the task of delivering ballast trains to Arlesburgh Junction for the standard gauge engines to take to the construction site. He was first seen by Marion when he was racing through the forest outside the junction, startling her. When she discovered who he and the other small engines were, both he and Rex explained how they delivered passengers and wool to the railway. After Thomas began feeling depressed when his branch line was taken away from him, Bert and the other two small engines sang "Never Overlook a Little Engine" to him to cheer him up, but this only re-aroused his overconfidence.
Later that evening, Marion returned to the junction to make a wish on the small engines. Bert and Rex both managed to escape in time, but Mike was trapped on the chute by her. Two nights later, Bert and the small engines were at the junction when they saw Sailor John and the pirate ship sail through. After Thomas requested their help, Bert helped Rex and Mike shunt a train of ballast hoppers onto the track, slowing the ship down. Bert and the other small engines cheered Thomas on as he chased after Sailor John. (TVS; Sodor's Legend of the Lost Treasure)
Bert is based on the Ravenglass and Eskdale Railway's "River Irt", a 0-8-2 tender engine that currently works on the line. River Irt was originally built as an eight-wheeled tank engine called "Muriel", but was rebuilt as a 0-8-2 tender engine after it was brought to the Ravenglass and Eskdale Railway in 1927. River Irt was once again rebuilt in 1972, giving it a taller funnel, dome and cab. Bert is based on River Irt's pre-1972 shape.
Bert is painted in the North Western Railway's blue livery with red lining. His dome and builder plates are both gold, and he carries two red nameplates with gold lettering on each side of his boiler. He also has the word "Arlesdale" written on the sides of his tender in yellow lettering with red outlining. Bert's footplate and wheels were originally painted black in the Railway Series, but when he was introduced in the television series, his footplate became light grey and his wheels were painted blue. He also received a permanent headlamp mounted atop of his smokebox and a lamp-iron on the right side of his footplate.
Starting with Jock the New Engine, Bert's driving wheels were built outside his frames, contrary to his basis and early Railway Series portrayal. His wheelbase also became longer, causing his front two driving wheels to be placed behind his cylinders. His valve gear was also changed because of this.
- Bert's rebuilt form has never been shown in either the Railway Series or television series.
- In both the Railway Series and television series descriptions, Bert is described as being younger than Rex and Mike. However, his basis was built long before either of them were, so it is very likely that he is also older than them.
- Bert shares his whistle sound with Mighty.