Neil was a dark green tank engine with an unusual box shape and a Scottish accent. He is a simple but kind engine, who befriended Skarloey when he was young.
Built at the Neilson and Company Works in Glasgow, Scotland in the 1860s, Neil was part of the Sodor and Mainland Railway and helped to ferry Skarloey from the port of Kirk Ronan to his home at the Skarloey Railway terminus of Crovan's Gate. Very little is known about Neil, or what happened to him following the amalgamation of the S&M with the other railways on Sodor to become the North Western Railway. He was most likely scrapped when deemed to be outdated or incapable of dealing with the more modern day workloads.
Skarloey said Neil was ugly but kind, and they soon became friends.
In Sodor: Reading Between the Lines, Christopher Awdry states that Neil's class is unknown. However, he strikingly resembles a Neilson 0-4-0 box tank, a simple and robust class of engine built in Glasgow and sold all over the world. This would explain both his name and his accent.
Neil was painted dark green with "S&M 2" written on his tank sides in yellow.