Merlin is an experimental tender engine who believes he has the power to turn invisible and has three funnels.
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 him 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.
When he first came to Sodor, he showed everyone he can become invisible, except Percy, who was upset he did not get to see him. When Percy heard an unfamiliar whistle in the distance but could not see who it belonged to, he assumed it was Merlin, and rushed off to tell Thomas. However, the "invisible engine" turned out to be Trevor.
Merlin sees himself as a hero. He is proud and confident of his abilities and in particular his special skill - the ability to make himself invisible. All he has to do is say "Invisibility on!" and shut his eyes and he is convinced that nobody can see him. He knows he was specially designed in order to be hard to see and his three funnels, which were intended to disperse his smoke and steam, are there to prove it. What Merlin does not know is that his experiment did not work. Merlin wants to be able to prove himself and show everyone all the things he can do. He honestly believes you can do anything you set your mind to or at the very least, you can try! Merlin is fun and funny and wants to be a good friend, but his lack of judgment and sense of his own limitations can create its own challenges.
Merlin is based on the LSWR N15 Class, referred to as the "King Arthur" class by the Southern Railway, specifically No. 783 Sir Gillemere. In 1940, Sir Gillemere was fitted with three stovepipe chimneys by Oliver Bulleid as a wartime experiment. The way the smoke was spread out was meant to make the trains less visible to bombers overhead. The experiment was not a success, and the engine was quickly converted back to normal. No. 783 became No. 30783 under British Railways after nationalisation in 1948 and was withdrawn in March 1961.
Merlin's name is likely taken from another King Arthur locomotive, No. 740 Merlin. A single King Arthur is preserved as part of the National Collection, No. 777 Sir Lamiel, and is based at the Great Central Railway, currently awaiting overhaul.
Merlin is painted silver with a red running board and wheels, and black smoke deflectors. He has red and gold nameplates on either sides. His number is also painted white on his front bufferbeam, the sides of his cab and tender.
- 2017 - Journey Beyond Sodor
- Hugh Bonneville (UK/US; Journey Beyond Sodor onwards, excluding Percy's fantasy)
- Nigel Pilkington (Percy's fantasy only)
- Kenta Miyake (Japan)
- Grzegorz Pawlak (Poland)
- Miguel Ángel Ghigliazza (Latin America; Journey Beyond Sodor only)
- Martin Lohmann (Germany)
- Kertesz Peter (Hungary)
- Merlin's whistle sound is of an LNER A4 Pacific 3-chime.
- Merlin's tender is a modified version of Bert's.
- Merlin is the second character to have his basis named in the show, with BoCo being the first.
- Merlin is currently the only character introduced in Journey Beyond Sodor to appear in an episode.
- The Trackmaster Merlin toy depicts him very metallic, unlike how he appears in the show.
- “I'm invisible! Or can't you see? Who said that? You ask. It's only me! You look surprised, but have no fear! It's just a little trick to make myself disappear!”
- ―Merlin's solo in 'We Can't Do Anything'
- “We can't do anything!"
"But we can try! We can give anything a try! We will give anything a try! Isn't that right?”
- ―Merlin responding positively to Lexi and Theo, Journey Beyond Sodor
- “This is my first time on the Island of Sonar, my friend Thomas works here."
"Do you mean Sodor?”
- ―Merlin and Cranky, Seeing is Believing