|Railway Series Portrait|
|Position||Arlesdale Railway engine|
|Age||88 (as of 2011)|
|Arrived on Sodor||Unknown|
Rex is a green tender engine who works on the Arlesdale Railway. He was built in 1923.
Rex told Bill and Ben about the Arlesdale Railway and its engines. He also told them about Diesel's angry behavior. On the day before the grand opening of the Arlesdale Railway, Rex and Bert was ordered by the Small Controller to take passenger trains. He was later told by Sarah the historian about Duke and what happened to him when the Mid Sodor Railway closed down. Rex later offered help when James' line was blocked by a tree, but the offer was rejected by Sir Charles Topham Hatt. He was later told about the famers' produce of wool. He later talked to Barry when he was collecting a train of ballast. He talked to Mike at the shed about Olivia before the green tank engine said about Sir Walter's own children having a disinterest to the estate railway.
In Cold Reception, he was told by Bert about Olivia's anger and Jane Albworth before the green tender engine spoke to Olivia about the woman at a lead mine where he was helping out with some construction work there before Olivia had arrived.
In Storm Damage, he, Olivia, Frank and Blister 2 were talking about the aforementioned storm, and how they couldn't contact Bert, Mike, Jock, Blister 1 and Sigrid. They also bring up The Old Mill and Atlas in conversation, not knowing they were one in the same.
Rex is based off the Ravenglass and Eskdale Railway's River Esk.
- Season 2 - Little Engines, Grand Opening and Whispers
- Season 3 - Useful Engines
- Season 5 - Harvest Season, Doubts and Sheffield's Secret (cameo)
- Season 1 STMY - Rough Start and Cold Reception
- Season 2 STMY - Food for Thought, Storm Damage, Dime For Trouble (stock footage, cameo), The Devious Way
- WildNorWester (STEY: Season 2 - Season 3)
- TheScotsmanReturns (Season 5 - Season 2 STMY Part 1)
- Bourbon-BobJimmy (STMY: Season 2 Part 2 onwards)
- In STEY, Rex was represented by the SI3D 2006 model. For STMY, he has a new model built according to the blueprints of his basis, River Esk.