Daisy is a Diesel engine that was built especially for service on Thomas' branch line. When she first arrived, she was highly strung and would only carry passengers because she felt she was too good to pull cargo cars. Daisy soon learned that all work is important on Sodor, and now helps out whenever she can.
Daisy was brought to the Railway after Thomas broke through the Stationmaster's house and "visited him" for breakfast. She is based on a diesel/mechanical single car passenger unit built by Metro-Cammel.