A friendly and enthusiastic front loader. Jack was first seen in the episode 'Jack Jumps In' when he joined the Pack. Despite a couple of accidents, he was able to prove himself when he saved Thomas from disaster, and is now part of the team. Jack is painted red and has the number 11.
It is unclear what type of vehicle Jack is based on, although he resemble a Nuffield Tractor. Concept artwork shows Jack with a backhoe.