Frank is a grumpy diesel who lives and works on 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 steampipe leaked and needed his train.
Frank means well and has a good heart, but can tend to be grumpy.
Frank is painted light grey with a red stripe and has red nameplates with his name in gold writing.