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. He wants to follow Milo because he wants a change from common life. In fact, he accepts going to school with Milo because his adventures are unique ("Going the Extra Milo").
He also wants to be safe enough though. In the episode Sunny Side Up, he has no problems on doing a science project with Milo, even knowing that it's extremely hard, but when they made it he didn't let Milo get near to make the project safe.
Maybe because he's new, he seems to not be fully aware of what Murphy's law can cause. He often says that things couldn't go worse, or he thinks that is some case, nothing wrong can happen. Zack is also fairly self-conscious about previously being part of The Lumberzacks, at times trying to conceal the fact from his friends while at others actually hoping to be recognized for the role.
Zack has dark eyes, brown skin, and thick, bushy black hair.
He wears a deep-yellow short-sleeved shirt over a white long-sleeved shirt, revealing only the collar and the sleeves of the latter, alongside a pair of light colored blue jeans with pockets and gray cuffs. His sneakers are a darker blue and white with white laces.
He is slightly taller than both Milo and Melissa and tends to stand with a bit of a slouch, giving off a 'chill' appearance. Likewise, he often sports a cocky, relaxed expression to the same effect.