Zack is a foreman's engine who helps mentor Brewster. Alongside Tyne and Fletch, they're known as the "Chuggineers", a railway maintenance team that works with the Crotoonian Construction Company on a variety of construction jobs on Crotoonia's railways. Preferring to keep things "Solid as a rock and perfectly aligned!", Zack is well-organized and makes sure everyone on the site works safe. He can lose his patience when things bother him or distract him, but he works hard and makes sure to keep his team in a solid working rhythm.
Zack is based on a GE Dash 9-44CWL diesel-electric hybrid engine.
Zack is painted blue with white stripes, red base, and an orange caution stripe between two big white caution stripes.