- "An old engine fell into sea. Versatile upon many degree. Elusive and vigilant he will always be. It is a self-fulfilling prophecy. Lamp in hand means I am no longer free, and chance you'll have to converse with me. In times of turmoil, keep my light, as sunny days fade into night. I am Proteus, an engine of the sea, an engine of the light, and cursed with the lamp of redeemable foresight. Find my rails if you hear my call. I am the savior of you all."
- ―Proteus' prophetic statement, Logan Leaves his Mark
Proteus is a ghostly spirit that roams the Skarloey Railway.
Proteus came to help on the Skarloey Railway before Peter Sam and Sir Handel's arrival. He was sent to work at the slate mines for his first day and did not finish until late at night. His headlamp was broken, and he had to cross the Old Iron Bridge without a light. Proteus fell off the unsafe bridge and plunged into the ravine and was never seen again. However, it is said that his spirit still roams free.
The older engines on the Skarloey Railway love telling stories about Proteus' lost lamp and his adventures as the ghostly spirit to the younger engines, who sometimes (like Peter Sam) take his stories to heart.
His lamp was discovered unknowingly by the Small Controller while on a search party for a lost sheep. He kept it in his office for some time.
Proteus warned Skarloey and his driver about the Old Iron Bridge's collapse, saving them from certain doom, but Skarloey, the driver, and fireman decided not to inform the Thin Controller and the other engines of this predicament.
In "All the World's a Stage," Sir Handel refused to act convincingly frightened. When it was time for him to take the stage, Proteus appeared before him, terrifying the little blue engine! However, the other engines just thought he had decided to put more effort into his acting at the last second.
Proteus appears regularly as a ghost, appearing, letting out his ghostly whistle, and then disappearing again. According to Sir Handel and Skarloey, Proteus' ghost has taken on appearances very similar to their respecitve prototypes, causing Peter Sam to speculate that Proteus is capable of shifting his ghostly form.
He was present for a uniting of destinies: One for a blue tank engine, and the other for the controller of the line he once worked for. Mysterious forces were at play, with Proteus seemingly being the architect of it all.
Later, his whistle echoes from his old lamp, now in the hands of an unsuspecting sheepherder, whereupon Proteus' voice rang forth a prophetic statement. Perhaps not by coincidence, Culdee had an accident shortly afterwards.
As the Shepherd wanders Sodor, the lamp etches the Man in the Hills into nearby cliffs. During one such incident, the electrical blast from the lamp knocks the Shepherd off the bridge over Poll-ny-Chrink. The wanderer dangles from the bridge with his crook in one hand and the lamp in the other. Initially refusing to let go of it, the Shepherd finally lets go of the lamp to save himself, tossing the lamp into the lake below.
Unwittingly, Oliver the Excavator discovers the lamp when digging near Poll-ny-Chrink following the incident. The lamp's mysterious aura prompts him to keep it.
During the events of Percy and Asbestos, Proteus seemingly takes the form of Blue Peter, using this persona to give Richard Hatt a lucky Blue Peter flag. Following this deed, Blue Peter mysteriously disappears near the Skarloey Railway, dissolving away as Proteus returns.
Proteus is mysterious, cheerful and mystical sort, and helps the narrow gauge engines in moments of need, especially in a moment of crisis, appearing to them as a ghost. He is also commonly seen roaming Sodor, and can be spotted if one has a close eye.
- Season 1: Lift Bridge (cameo), The Old Warrior (cameo), Double Whammy (cameo), Cannon Fodder (cameo), Greg and Lars (cameo)
- Season 2: Breakdown Blues (cameo), Two Hearts Burn Together (cameo), Pigeon Hunting (cameo), Mavis and the Tornado (cameo), Rosie (cameo), Just Another Wild Goose Chase (does not speak, unnamed), Munitions (cameo), Blunderbuss (cameo), Luke and Millie's Blue Mountain Adventure (cameo), All the World's a Stage, Swashbuckler, Dead End (whistle only), Thomas and the Fortune Teller (does not speak), Self-Fulfilling Prophecy
- Season 3: Logan Leaves his Mark, Samson, BoCo, and the Man in the Hills (cameo), Culdee Fell, Chivalry is Dead (cameo), Percy and Asbestos (does not speak), Merrick's Wake up Call (cameo)