Frank is a grumpy diesel who lives and works on the Arlesdale Railway.
Frank was constructed at Arlesburgh Works circa 1967 out of bits and pieces from several other engines. He is powered by a Perkins diesel engine, and was named after its creator. He is a shunter who is used for maintenance work and empty carriage workings across the Arlesdale Railway.
When Small Railway Engines was first published, Frank became infuriated when he found out that he had been left out due to the Thin Clergyman not being aware of his presence. He then refused to come out of the shed the next morning, but when he did, he only resulted in running into the back of the shed, cracking a shed support. He then felt ashamed of what he had done, but later redeemed himself by rescuing Rex when his steam pipe leaked and taking his train. Believing Frank shouldn't have to do rescues, the Small Controller realised the railway needed another engine, which came in the form of Jock.
Frank means well and has a good heart, but has a tendency to be grumpy.
Frank is painted light grey with a red stripe around his body. He has red nameplates with his name in gold on his sides.
- He is named after Frank Perkins, the engineer who created the Perkins diesel engine.