Duncan has also been very cocky, but this has often fired back at him. His driver and fireman spooked him one evening when fireflies formed the shape of an engine. This put Duncan in his place, thinking he had just seen a ghost. His ego once landed him in a swamp, after being careless working on the incline railway.
Duncan is well known and often teased for his temper. He has met his match before, a passenger who grumbled more than him! Despite his rough exterior, he heroically helped Luke up a hill around Christmas time, showing his kinder side.
Duncan is a Scottish narrow gauge engine with rough manners and a strong temper. He was prone to boisterous bouncing about, which became known as "rock 'n' roll", whenever the mood took him, which once led to wedging in the north mouth of Rheneas Tunnel (probably caused from keystones knocked down by his funnel) and derailing on a stretch of line near Cros-ny-Cuirn. While Duncan means well, he often grumbles and complains, usually about not being polished or being over-worked, and can be rude, rough, and bad tempered. He claims to be a plain-speaking engine who believes in plain speaking, an approach which can cause him to make callous or belligerent remarks. Duncan can be a competitive engine too, particularly with James. He can be careless and make rash decisions which usually leads to his own downfall, (such as getting in arguments or short lived feuds with Rusty) but is not always quick to apologise or realise the error of his ways. However, upon Skarloey recalling Rheneas' gallant act to get his passengers home, Duncan admitted he had the wrong attitude and tried hard to be a more useful, respectable engine in future. In spite of his ways, Duncan can be a little misunderstood as he is focused, confident, resourceful and has a big heart. He is always willing to lend a helping hand whenever he can.
Duncan is based on the Talyllyn Railway's Douglas, an Andrew Barclay 0-4-0WT. This engine is currently selected to be dressed up as Duncan on special events associated with the "Thomas the Tank Engine" franchise.
Duncan is painted golden yellow with black lining and gold boiler bands. He has brass, originally black, name and numberplates on the sides of his boiler and cab respectively.