- “I have no spare whistles, so you'll have to wait! It serves you right for being such a crosspatch!”
- ―The Small Controller scolding Mike
Mr Fergus Duncan, nicknamed the Small Controller is the General Manager of the Arlesdale Railway. He is actually taller than the Fat Controller and the Thin Controller; his nickname refers to the fact that his railway is often called the "Small Railway".
Fergus Duncan was born in 1936. In 1965, a consortium was formed by the managements of the Sudrian railways to build a new railway to exploit a source of ballast on the closed Mid Sodor Railway. Fergus Duncan was appointed to oversee the construction of the line, the Arlesdale Railway, which went ahead rapidly under his direction. Upon the line's opening at Easter 1967, he was appointed its General Manager. He lives in a house which he built himself at Arlesdale Green, near the station and his office is located at Arlesburgh West.
Around 1977, he adopted a system of Radio Control for his railway, on the suggestion of its basis, the Ravenglass and Eskdale Railway. By 1987, the system had worked almost perfectly and had the conditional approval of the Railway Inspectorate. Fergus Duncan, however, had no doubt of the final outcome and was looking forward to the day when the other railways on the Island are recommended by the Inspector to follow the Arlesdale's lead.
In 2005, he was approaching a remarkable 40 years of service to the line. Despite nearing 70, he was still hale and hearty, but he had let it be known he intended to retire on achieving that landmark in 2007. It is felt in many quarters that the example set in his service to the line will be a difficult one to follow.
The Small Controller is very passionate about his work and never married. He preferred instead to devote his life entirely to work on his railway.
Like every other controller of their own railway on Sodor, he acts as a fatherly figure to his engines and always knows when to be stern with them should they misbehave.
Fergus Duncan's attire consists of a yellow waistcoat over a white shirt with a red tie and a brown jacket over it, with mustard windowpane chequered trousers. He wears a yellow flower on his jacket.
- Small Railway Engines - Ballast (mentioned), Tit for Tat, Mike's Whistle and Useful Railway
- Duke the Lost Engine - Sleeping Beauty
- Jock the New Engine - We Need Another Engine, Jock and Teamwork (not seen)
- 1987 - The Island of Sodor: Its People, History and Railways (mentioned)
- 2005 - Sodor: Reading Between the Lines (mentioned)
- Rob Rackstraw (UK/US)
- Kenta Miyake (Japan)
- Wojciech Chorąży (Poland)
- Óscar Gómez (Latin America)
- Gadi Levy (Israel)
- In Sodor: Reading Between the Lines, he is referred to as Francis Duncan.
- Unlike Sir Topham Hatt and Mr. Percival, he is referred to by his nickname in the US version of the television series.
- The Small Controller is based on Douglas Ferreira, who was the General Manager of the Ravenglass and Eskdale Railway from 1961 to 1994, in which a new diesel locomotive was built and named in his honour in 2005.