Rex is a small green tender engine who lives and works on the Arlesdale Railway. He enjoys nothing more than teasing Mike. He is a hard worker, but sometimes has problems with traction.

Rex is a playful green miniature engine with a strong sense of humour. He is a hard worker, and is the natural leader of the little railway engines (in spite of the fact that Mike prefers to think he’s the leader). Rex is very proud of his railway and a great friend to the other engines, but he can’t help teasing Mike to stop him getting too full of himself. Most of the time Mike manages to return the banter, but sometimes he gets a little wound up. Luckily Rex is very good at helping Mike see the funny side again. He does have a kind side and is generally kind hearted and friendly.