*Daisy is a green diesel railcar who came to work on the Ffarquhar Branch Line. She now works on the Harwick Branch Line carrying out passenger duties, while Ryan runs the goods duties.

Daisy is a diesel railcar, who has been known to consider herself "highly sprung and right up to date". She was brought to help run passenger services on Thomas' Branch Line, while Thomas was "indisposed" after running into the Tidmouth Stationmaster's House. She can be hard to please, mostly indignant and highly opinionated. She is extremely authoritative, trustworthy and confident in herself and can sometimes boast of her abilities in particular situations, unconcerned, despite having never actually been in such a position before. She will sometimes presume she can show other engines a thing or two, despite knowing little on the matter, until she actually learns for herself.

After arriving on Sodor, Daisy insisted that she required delicate handling and considered pulling trucks and vans to be below her. She was very lazy and stubborn, but the Fat Controller spoke severely to her, telling her that his engines must work hard and that he sends lazy engines away. However, the Fat Controller felt she deserved another chance after she worked hard clearing up after an accident Percy had. Daisy is now good friends with the other engines on Thomas' Branch Line, tries to work much harder to be a Really Useful Engine and is better capable of handling things alone. She can be described as a self-obsessed diva and is also vain about not wanting her interior to be dirty one bit.

Despite changing for the better, Daisy is still snarky and irritable. During the steam engines' feud with the diesels, she temporarily sided with the diesels in their hatred of all of the steam engines. Generally, though, Daisy is one of the more well-behaved diesels, as aside from minor squabbles she gets along with the Ffarquhar branch line residents rather well.

In newer episodes, Daisy was heard speaking French, such as when she said "Merci beaucoup" (Thank you very much) to Den and Dart after she was repaired, and when she used the terms to describe the entertainers she was to carry to Duck and Oliver, which indicates that she has knowledge in the French language as well. She also matured greatly in a number of recent episodes, as she rarely made brooding remarks or patronising comments, and instead began trying to help others. Despite her increased maturity, Daisy's snobbish side is still very prevalent, as she still belittled Thomas, Annie and Clarabel on more than one occasion.

While Daisy is typically well aware of how things are supposed to be done on Sodor, her ego can leave her to cast out common sense in favour of selfish vanity, often to the utter fury of passengers, engines and crew alike, especially when the manner in question can be done trivially. This can turn away people who have previously admired her, and often leads to reprimanding from others.

Daisy is based on the diesel multiple units (DMUs) built by Metro-Cammell for British Railways (BR), albeit as a single railcar instead of the traditional two- to four-piece units. In particular, she is based off of the BR Metro-Cammell "Lightweight" units and the BR Class 101 DMUs.

In the model series, Daisy notably differs from her basis, having much lower buffers and her main passenger compartment being significantly shorter in height. This is due to her having to be built to fit on top of BoCo's chassis.

Daisy is painted green with yellow stripes and red bufferbeams. She wears makeup, including eyelashes, pink lipstick, blush and eyeshadow (blue in the model series, lavender or mauve in the CGI series).*