Theo is an experimental railway traction engine.
When Thomas travels to the Mainland, he befriends the experimental engines, Theo, Merlin and Lexi. Later, the experimental engines come to rescue Thomas and James when they are trapped in the Steelworks.
Geared engine Theo is very shy, extremely cautious and awkward. He has an unusual experimental drive system that doesn’t always run very smoothly and he makes sudden jolts forward or back when his rods or cogs jam. Quiet and thoughtful, with a habit of blunt speaking, his confidence is often jolted. But Theo is genuinely kind and caring and would just like to keep himself and his friends as safe as possible so they can hide away and have a quiet life.”
Theo appears to be a hybrid between the Coalbrookdale locomotive, an early steam engine built by Richard Trevithick, and the Aveling and Porter 2-2-0WT 'TJ' class railway traction engine No. 9449 "The Blue Circle", Fergus's basis.
Theo is painted greyish brown with gold lining, head lamp and whistle. His wheels and lower traction wheels are dark green while his upper traction wheels are a redish brown. Theo also carries his name on gold nameplates fixated on each side of his smoke box.
- Thomas and Friends Adventures (coming soon)