When Thomas travelled to the Mainland, he befriended the experimental engines: Lexi, Theo, and Merlin. Thomas encountered Lexi and Theo in an empty yard, where he was warmly welcomed and refilled with coal. Later, Lexi, along with the other experimentals, helped Thomas rescue James, who had been trapped in the Steelworks.
Afterwards, Thomas encouraged Lexi (along with Theo and Merlin) to stay with Frankie and Hurricane and call the Steelworks their new home.
Lexi is an eager and excitable engine. She is proud of being experimental and 'cab-forward'- even though she is convinced this makes her an un-useful engine.
Lexi is upbeat, cheery and outgoing, and likes to experiment with how she presents herself, often trying out different voices and how she phrases her expressions just to see which one she thinks works best. Lexi is not always confident she gets things right, but she loves the excitement of anything new, is very sociable, and keen to explore new things.
Lexi is based on the North Pacific Coast Railroad Cab-Forward 4-4-0 No. 21 "Thomas-Stetson", a rebuild of NPCRR #5 which had been wrecked in 1897. An innovative engine built by Bill Thomas, it is considered the first cab-forward locomotive and was one of the first oil burners, as well as the first locomotive to use a marine boiler. The engine had insufficient adhesion weight and its oil burners were prone to damage due their proximity to its water tubes, and was unpopular with crews, its unusual appearance earning it the nickname "The Freak". #21 was scrapped in 1905.
Lexi is painted light turquoise with a gold cowcatcher. Her front windows have gold lining, and her side windows have copper lining. Her main body is covered in rust. She has brass nameplates fixated on each side of her cab and the initials "N.P.C.R.R" painted on her rear oil tank.
- 2017 - Journey Beyond Sodor.
- Lucy Montgomery (UK/US)
- Kazuko Kurosawa (Japan)
- Marta Dobecka (Poland)
- Katharina von Keller (Germany)
- Csondor Kata (Hungary)
- Lexi has received several modifications compared to her basis:
- Lexi has been modified to accommodate a face, as a lamp would actually be where her face is. Her lamp has also been moved to her added footplate.
- She has been modified for working on British railways with the addition of buffers and a screw-link coupling on her tender, as well as brake-pipes on her front and back.
- She has been regauged from 3ft gauge to standard gauge.
- Lexi seems to speaks with a Scottish accent and imitates many other dialects, despite being based on an American engine.
- Lexi's tender wheels are actually reused from Marion's wheels, and her bell is reused from Belle's bell.
- Lexi shares the same whistle sound as the Rainbow Sun and Carlos.