Carl is a diesel that works on Oliver's old line. He hates steam engines and wants to see them all scrapped, much like his owner. Carl suggested that Oliver should be cut up elsewhere due to the Steam Excursion arriving later that day, but instead be repainted to BR colors to be unnoticed.
Carl is based on a British Rail Class 56.
- In the script, Carl was called 'Anon Diesel', due to not having a name at the time of writing.
- The name "Carl" came from the TV Show The Walking Dead. The idea for the name came from Carl's Voice actor, JD41796, while he and Ilovetrains323 were watching at the time of production.