- "You know, your voice gets all high-pitched and squeaky when you're angry. It's kind of adorable."
- ―Mike, Sidney
Frank is a small grumpy grey diesel who works on the Arlesdale Railway.
Frank is a grumpy gray diesel. He works with Mike quite often at the Ballast Hopper where they load trucks for the Little Western Engines. Frank can be overly sensitive and can get annoyed very easily, and Mike takes pleasure in infuriating him. His voice gets very high pitched and squeaky when he's angry. Despite everything, Frank is diligent and only wants to make a name for himself, and he values his time with Mike much more than he would let on!
When Oliver arrived at the chute during "Lift Bridge," Frank was cross at Mike for implying that he only existed for Mike's entertainment. Oliver laughed, and left the two "lovebirds" to argue.
Later, he and Mike were arguing about sheep, automobiles, and traffic, when Stepney fell from the sky, landing right in front of them!
While Mike was on a search party, Frank was pulling a ballast train. He stopped to talk to a farmer, but Mike, who had no light, crashed into his trucks! Frank criticized Mike, but the two suddenly realized that the lost sheep Mike was looking for was standing above the wreckage!
On a later occasion, Frank was cheerfully clattering along, when he realized that Donald had knocked a bridge over! He wasn't able to stop in time and crashed next to Donald, and was very cross at the Scottish engine for his clumsy accident.
When Sidney first arrived, Frank was horrified and humiliated that his fellow diesel was such an imbecile! He quickly took a strong dislike to Sidney, but after Oliver assured him and the others that Sidney meant well, he did his best not to be rude.
During the tornado incident, Frank was relieved that the Extension Bridge had not fallen on him, and after a quick insult from Mike, quickly fled the scene.
When Mike told Stanley the story of his whistle, Frank assured Stanley that the event was hilarious.
In "Swashbuckler", Mike and Frank attempt to give The Small Controller romantic advice, with Frank making a point that if he "didn't always smell of Tidmouth Kippers" he'd have better luck getting dates. This notion was obviously not recieved well.
- Season 1: Lift Bridge, Stepney Makes an Entrance, Search Party, Rising to the Occasion, Snow Blind (flashback cameo), Sidney, Conspiracy Theory (cameo)
- Season 2: Mavis and the Tornado, Waterworks, Rock-Star (cameo), Swashbuckler
- Season 3: Stafford's Request (cameo)
- Web Clips: Rex, Bert, Mike and Frank - Meet the Characters!, Mike and Frank Banter: SLOTLT, ScarletFire, and EE93's Return
- Both he and Mike are voiced by Enterprisingengine93.
- Collectively, Frank and Mike have never spoke in an episode without one another (although the latter has had more cameos)