Merlin is an experimental tender engine who believes he has the power to turn invisible.


When Thomas travelled to the Mainland, he befriended the experimental engines: Merlin, Theo and Lexi. Merlin sails through life, full of confidence, believing that he has the ability to become invisible. Helping to hide Thomas from Frankie and Hurricane, he promised to help Thomas find his way back to Sodor. Later, Merlin, along with the other experimentals, helped Thomas rescue James, who had been trapped in the Steelworks.

Afterwards, Merlin offered to stay at the Steelworks to help Frankie and Hurricane and helped Thomas to convince the other experimental engines Theo and Lexi to do the same.