After Rex's steampipe began leaking one day and Frank had to take his train, the Small Controller began thinking they needed another engine and so he arranged for Jock to be built. When Jock first came out for testing he was still unnamed. Jock's paint colour reminded Douglas of his days on the Highland Railway and suggested the name "Jock" for the new engine. The Small Controller and Jock liked the name so it stuck. Later, he pulled a doubleheader with Mike.
Jock was very cocky when he was first built, as a result of being rather strong, but soon learned the value of teamwork when Mike's injector failed and he had to pull Mike and his train single-handedly.
He will appear in Season 3.
- Because the Thomas Wooden Railway line never made a model of Jock, EE93 used Jock as a custom model made by Turtlesandthomas. It was made from a 2013 wooden railway model of James with Emily's tender.