*Nia is an orange tank engine from Kenya who lives and works on the Island of Sodor, and is the North Western Railway's number 18 engine.

Nia is an adventurous and fun engine who taught Thomas - and even Gordon - about friendship and new things during her new beginnings. Whether she is in her homeland of Africa or travelling around the world, Nia is positive, kind-hearted and caring. Her eagerness to help can sometimes irritate her friends, but her truthfulness and kind heart always win them over. She is a good problem solver, although she once had trouble reading numbers until Annie and Clarabel helped her. Nia can be very sensitive about being abandoned or ignored, and this can quite often make her give someone the cold shoulder if they maintain this type of behaviour, especially if someone is acting very rude. This does not stop her from befriending others though, and aside from playful retributions she will happily forgive any offenders if she feels they are truly sorry.

If Nia has any significant flaw, it's that she can sometimes be too eager-to-please, or optimistic to the point of naivety. She is also self-conscious about being seen as a competent, capable engine, and hates looking silly in front of others.

Nia is based on a Kenya-Uganda Railway (KUR) ED1 class, a class of 2-6-2 tank locomotive built by Vulcan Foundry for the Kenya-Uganda Railway between 1926 and 1930. Primarily used for shunting duties, they were also used to haul branch line trains. They were later operated by the East African Railways and were reclassified as part of the EAR 11 class. One member of this class, No. 327, has been preserved at the Nairobi Railway Museum in Nairobi, Kenya. Nia's design sheet shows that she was specifically modelled after No. 327.

Nia has been modified in order to work on British railways. Whereas her original basis was metre gauge, Nia is standard gauge and she has been given buffers and screwlink couplings in order to work with the other engines.

Nia is painted orange with yellow lining. She has stripes with a Kenyan pattern consisting of red, yellow, green, black and purple painted along with her tanks and dome, as well as green and yellow lining on her cylinders. Nia has green stripes on her boiler and brake pump. Her footplate is painted red with black buffers. Her name (Nia) and her number (18) are painted on the sides of her tanks and cab respectively in yellow within black squares.*