Zack was a nice young boy who enjoyed working on his Mech in a garage. At one point, along with most of the citizens of Steamworks Island, Zack was frozen so that he would survive when the Plant Mutations escaped. He was later found by you during the events of Steamworks Island.
You first see him when Sprocket asks you to help him find Zack and projects a hologram of him. When you find him, he is frozen with most of the citizens of Steamworks Island. You free him and destroy the Plant Monster Brains.