Montague (affectionately known as "Duck" because of his supposed waddle) is a Great Western 57xx pannier tank engine. Previously being the station pilot at Tidmouth, he now has his own branch line that runs between Tidmouth and Arlesburgh and is commonly seen working with Oliver.
In the Railway Series, Duck has two Great Western autocoaches named Alice and Mirabel. In the television series, he has three Great Western Slip Coaches, collectively nicknamed "Slippies".
Duck worked at Paddington before moving to Sodor in 1955 to take over Percy's shunting duties, leaving the latter free to assist with the construction of Knapford Harbour. Duck was a hard worker, but the others mistook his work ethic for simplicity and tried to use this to their advantage. They soon found their mistake when Duck and Percy took revenge on them by barring them from the shed. Duck earned a reprimand from the Fat Controller for this.
When Diesel arrived, the others took a liking to his flattery, but Duck was doubtful and left Diesel to his own devices, which resulted in the latter getting into a mishap with some old trucks. Duck tried to help Diesel when the trucks started to tease him, but to no avail. Diesel vowed to get revenge and inspired by several incidents occurring around the yard in Duck's absence, spread rumours that Duck had given offensive nicknames to the others. Duck was sent to work as a banker at Wellsworth pending further inquiry and after bravely stopping a runaway goods train at his own risk regained the respect of the others. Of course, by this time the others were aware that the matter was all Diesel's fault, but Duck's heroism certainly helped.
Duck would later show Donald and Douglas around when they arrived and they soon became friends. He also allowed Stepney to take a special visitor, and helped him double-head a passenger train when the Diesel broke down from sucking an inspector's hat into his air-intank. When Peter Sam told Duck about a duke coming to Sodor, Duck tells him that all dukes have been scrapped, causing him to worry. Whether or not Peter Sam meant that it was the Duke of Sodor or the engine Duke, Duck was most likely unaware of what Peter Sam meant, but as Skarloey had put it, Duck was probably pulling Peter Sam's wheels.
Duck continued working on the Main Line until 1967. When Donald and Douglas brought in new ballast for the track, they mention that "verra wee engines" that bring it down from the hills. Duck was curious about this and asks to take some trucks along the line that is later known as the Tidmouth-Arlesburgh branch line - nicknamed The Little Western. It is there that Duck meets three small engines, Rex, Mike, and Bert, all who bring in the ballast and helped restore the branch line. Duck was later asked to run it with help from Oliver and on occasion, Donald and Douglas.
One time, a double decker bus named Bulgy tried to steal Duck's passengers, but got stuck under a bridge where Duck encountered him. When his passengers realised that Bulgy lied to them by saying he was a railway bus and accepted railway tickets, Duck managed to regain his passengers, and made it safely across the bridge, where he brought the passengers home in good time. Bulgy, however, was turned into a henhouse close to his line.
Duck would later help Henry with the Flying Kipper as a banker, only to end up crashing into his rear trucks when the tail lamp fell off. He also helped Thomas and Percy triple-head the express when neither Gordon nor Henry could do it.
Later, Duck was trapped at the docks with the big engines and Cranky. A tramp steamer crashed into the shed causing the shed and Cranky to topple over while also causing the engines to be trapped. Luckily, Thomas and Percy rescued them. Afterwards, George refused to let Duck get his truck off the Main Line, resulting in Gordon crashing into it. Duck was spared punishment when the Fat Controller was told George was to blame for Duck not clearing the Main Line before Gordon came through.
Sometimes it appears the Fat Controller has deputised Duck at other places on the railway. He has been seen in various yards along the Main Line and Edward's Branch Line doing mostly goods work.
When Harold broke down at Callan Castle, Duck was asked to take him to the Sodor Search and Rescue Centre for repairs, with Thomas as his back engine. However Thomas wanted Harold to see the sights of Sodor, so he tricked Duck into going to Knapford. After this, Duck became cross with Thomas. Thomas tried to warn Duck about a narrow tunnel up ahead, but Duck took no notice and ended up damaging Harold's rotor blades. After this, the two engines made up and worked together to deliver Harold to the rescue centre.
He once ran into a flood whilst working on his branch line and had to wait until James brought Rocky to help him. Unfortunately, Oliver and Percy ran into them due to a broken signal knocked down by Rocky's swinging crane arm and delayed Duck's rescue. During one hectic summer, the Fat Controller was not sure how to handle the number of passengers travelling on his railway. Duck suggested bringing slip coaches, which he had used on the Great Western Railway, to the island. However, James lied and used the idea as his own, initially receiving praise only to cause trouble. Duck soon took control of the slip coaches and things worked out perfectly, with the coaches now appearing to be used year round. He later ran a red signal by mistake while trying to show how fast he could be and almost collided with Oliver.
In 2015, Duck helped with building the new Harwick Branch Line and was very excited and surprised to see Donald and Douglas whom he had not seen for ages. He later brought Rocky to lift Thomas out of the cavern that he had fallen into and sometime later attended the branch line's opening ceremony.
In 2016, Duck and the Slip Coaches nearly collided with Ryan while the purple tank engine was taking passengers and a mail truck for Daisy at the same time. Later, Duck is taking the passengers home to make one more run to Arlesburgh and he stopped the fallen tree by Skiff after the lightning hitting the fallen tree.
After 2016, Duck along with all of the Fat Controller's engines wanted to go to the Great Railway Show, however he was not chosen.