Donald and Douglas are twin Scottish mixed-traffic engines. Donald and Douglas were built by John F. McIntosh and worked on the Caledonian Railway in Scotland, a large network that extended along the country's east coast as well as the central and south-western regions. Despite being limited to Caledonian metals, they appeared to have a familiarity with other railways, as they were familiar with the locomotives and livery of the Highland Railway.
- Donald and Douglas' drivers are related.
- On the Take-n-Play model check list Douglas's tender is backwards and reversed.
- In the Railway Series, Donald and Douglas are blue.