Zack Underwood is one of the deuteragonists of Disney XD's Milo Murphy's Law. The former lead singer of the boy band known as the Lumberzacks, he is the best friend of Milo Murphy and Melissa Chase. Although Zack enjoys hanging out with Milo due to his abnormal life, he also usually serves as the voice of reason when things get out of hand.
- Zack is the new kid in town and the voice of reason when things get out of hand. While the rest of the town is used to Milo, Zack is trying to enjoy the adventure of being Milo's best friend without getting destroyed.