- "If I were under me own power, I'd burst ye both to smithereens! Courtesy of Scotland!"
- ―Douglas threatening 'Arry and Bert, Lift Bridge
Donald and Douglas are two Scottish twin engines who do odd jobs and goods work on the branch lines.
Donald and Douglas came to Sodor to help out with the goods work, but only one engine had been expected. After causing a great deal of confusion, swapping numbers, destroying a signalbox, and demolishing a spiteful brakevan, the engines eventually secured their position on the railway. Invaluable in a blizzard, the two engines are renowned for rescuing engines trapped in fallen snow very efficiently!
Donald and Douglas began arguing with 'Arry and Bert when the Fat Controller made his announcement about the Tidmouth Lift Bridge's construction. Edward tried to calm them, but they refused to listen.
Donald was quick to recognize Bertram the Old Warrior's worth. A few days into his duties at The Mine Junction, he smashed a short line of troublesome trucks into the supports of High Tower and almost caused it to collapse on Toby. Thankfully, despite his doubts of the little engine's ability, Bertram quickly saved the day!
Donald and Douglas collectively destroyed two sets of buffers within two days.
The twins reassured a hesitant Oliver of Scruff's capability when he came to help at The Little Western Extension. Later, when Scruff was struggling to move a line of trucks, the two egg the shunter on and cause him to push the trucks over a cliff. The two then regret instigating him, and Douglas goes to get Rocky to retrieve the trucks form the ravine.
When Douglas' firebars collapsed, Sidney had to come to his rescue. Douglas quickly saw the value of the confused little diesel when he accidentally ran over the wrong switch, allowing Oliver's runaway train to roar past, preventing a disastrous collision!
Donald and Douglas, though often jokingly rude to Doc the Ballast Spreader, were infuriated with Percy's behavior when he mocked ballast as an art form.
Donald was in need of an overhaul, and was feeling put upon with work, when Bill and Ben decided to play a trick on him, deciding to lie and tell him that his line of cars were waiting in a siding on a cliff halfway around the island. The siding buffers however, were in need of repair, and when Donald came puffing through, he broke through the damaged buffers and flew off the cliff! Douglas, upon hearing of this news, went on a rampage, hunting the Bill and Ben down, eventually finding them at Crock's Scrap Yard. Edward needed to shunt a scrap truck in front of Bill and Ben to keep Douglas from possibly destroying the twins in his rage. Douglas spoke harshly about BoCo and Derek, claiming Bill and Ben could "bash them over the rocks whenever you want", referring to accidents the tank engine twins had caused earlier. Infuriated, he continued to hurl threats at the twins until Edward and Reg thankfully calmed him down. Douglas apologized for his behavior towards Boco and Derek, but did not give one to Bill & Ben, and stated that he would accept the apology they gave to him, eventually, before leaving.
Due to the loss of some of Donald's official paperwork, Douglas had to be taken off of work to be used as a reference in both repairing Donald and getting himself an overhaul.
Edward came in to check on the two's progress, meeting with Douglas, as he had just had his boiler replaced. After checking in on his state of mind, he asked if he saw Derek picking up Culdee, to which Douglas began to disparage diesel engines, stating he had no trust for diesels beyond BoCo and Sidney. Edward managed to remind him of his coming to terms with his anger following Donald's accident. After considering Edward's reminder, Douglas thanked Edward for his visit.
Despite not being physically present, Donald and Douglas both heard of Richard Hatt's idea of a suggestion box, as well as an attempt to ban Auld Lang Syne at social events via said box. The twins managed to get a suggestion to lift the ban, much to the disappointment of their fellow engines.
Donald and Douglas are practical, peppery, and proud. They work hard, and stand no nonsense from others. They love playing jokes all the same, and are not to be trifled with! They are some of The Fat Controller's most versatile and reliable engines, usually called upon to make ends meet and do odd jobs. They have a bit of prejudice towards diesel engines, but once they get to know them personally, they tend to warm up to them.
- Donald's 1992 model was replaced in "The Old Warrior."
- When John Muste was unavailable during the remastering of Scruff's Scaffolding, Richie Damico filled in as Donald and Douglas's voice actor.
- Season 1: Lift Bridge, Swagger and Swerves, Splatter (cameo), Stepney Makes an Entrance (Donald only), The Old Warrior (Donald only), Redemption (Donald only, cameo), Bon Voyage (Donald only, cameo), Improvisation (Donald only), Rising to the Occasion (Donald only, Douglas mentioned), Snow Blind (Donald only, cameo), Shepherd's Pie (cameo), Buffer Bashing (Donald does not speak), Scruff's Scaffolding, Wilbert the Lumberjack (cameo), Will Power (Donald only, mentioned), Sidney, Conspiracy Theory (cameo in flashback)
- Season 2: Paxton and Norman (Douglas only, cameo), Two Hearts Burn Together (Donald only, flashback, does not speak), Serendipity (Douglas only, cameo), Scot-free (Douglas only), Mavis and the Tornado (Donald only, cameo), Rosie (cameo), Waterworks (Donald only, cameo), James Goes on a Trip (Douglas only, cameo), Rock-Star, Pummeling Percy, Tag-Team (Donald only, cameo), Hibernation (Douglas only, cameo), Swan Dive (Douglas only, cameo), Swashbuckler (cameo)
- Season 3: This Too Shall Pass, Perhaps He's Got a Corset (mentioned, Donald appears in a flashback), Logan Leaves his Mark (Donald only, mentioned), Samson, BoCo, and the Man in the Hills (do not speak), Culdee Fell (Donald does not speak), Derek and the Two Faced Engines (Donald only, flashback, does not speak), The Suggestion Box (mentioned), Penn Pals (do not speak)
- Web Clips: Timothy, Bill, Ben, and Marion - Meet the Characters! (Donald only, cameo)