When Jack first arrived on Sodor he worked with the Pack to clear room for railway lines. Jack did well with Alfie - that is, until he tried to take some stone up a ledge but lost balance and rolled over. Jack learned his lesson, and redeemed himself by holding up a collapsing bridge until Thomas had passed over, at the cost of damaging his arms. Jack has since become part of the Pack.
He, along with the rest of the Pack, helped with the restoration of Great Waterton and worked with Alfie to construct a bandstand there.
A magazine fact file states that he now works at the Sodor Slate Quarry.
Jack was like a toddler at first, who was still learning about the world and how to stay out of trouble. He is brave and won't take any hassle, as seen when he stood up to Max when the latter was bullying him and Alfie.
It is unclear what type of vehicle Jack is based on, although he does resemble a Nuffield tractor.
Jack is painted red-orange with the top half of his cab painted cream. He has his number painted in white on his sides.
- In some promotional sketches of the Pack, Jack is seen with a backhoe arm and bucket. According to an SiF interview with Chris Lloyd, the arm was built, but was too problematic as it was hard to store all of the radio gear inside the model. An interview with Phil Fehrle gives a very different reason: "...if a story required Jack to be digging (using his back-hoe) and interacting with another character working at the same time, his face would be facing away from the action. For story purposes, it was important to feature the faces as much as possible; thus, the back-hoe was removed."