Theo is a very shy, extremely cautious and awkward geared engine. 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, along with his friends, Lexi and Merlin, Now work at the Mainland Steelworks with Frankie and Hurricane.
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 will appear in the series soon.