Zack Underwood

Zack Underwood is one of the deuteragonists of Disney Channel'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 the love interest 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.

Personality
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.

It is possible that because he's new in Danville, 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.

Physical Appearance
Zack has dark brown 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.

Marcus Underwood
Zack expressed his worries to his father when they went on a fishing trip with Milo and Martin. While Marcus did not initially believe his son over the existence of Murphy's Law, the two of them ended up working together to get the boat to shore. His father loves to scare him constantly- and would do so every Halloween, coming up with creative new ways to scare him every year. Zack loved this and claims it was awesome. His father manages to do it again recently despite Zack's belief that Halloween no longer scares him.

When Marcus doubts his abilities to help out on his uncle's farm, Zack reacts negatively, even telling his friends about how his father didn't think he could handle it. After he succeeds in doing all of the farm chores, he is excited to share it with Marcus and shows him various pictures from their day.

Eileen Underwood
He was happy to visit his mom on career day and seemed satisfied when the other students noted how cool her job was. Eileen went with him when the school had a parent-teacher night, and the two of them exchanged friendly banter before the meeting.

Cornelius Underwood
Cornelius is Zack's uncle. Zack was happy to see his uncle, who greeted him with a bear hug, calling him his 'favorite nephew'. Zack was eager to prove himself by helping out on his uncle's farm doing various chores, but when his uncle asks him if he can handle it, he points out how much Cornelius sounds like his dad, who didn't believe he could do it either. Zack is thrilled when his Cornelius points out what a good job he'd done on the chores.

Zelda
When looking for a solution to their problem getting a good picture of Milo, Zack quickly remembered that his cousin works as a passport photographer, and immediately recommended her for it. He has a lot of faith in her ability to take a good picture, and was happy to greet her when they met at the airport.

Milo Murphy
Zack and Milo are best friends. While Zack didn't initially want to spend time around Milo over his condition, Milo's optimistic attitude won him over, and the two of them have been close friends ever since. Zack has a very cautious attitude and tends to worry a lot, but he doesn't mind the adventures they go on, and enjoys spending time with Milo. He often gives a voice of reason to Milo's carefree attitude, pointing out the worse parts of their plans and voicing his fear when tempting fate by doing things that might invite danger.

Melissa Chase
He became good friends with Melissa through their mutual friendship with Milo. Melissa often tries to get Zack to loosen up while Zack tends to worry about Melissa's absent-mindedness. As Milo's best friends, they share in the difficulties of dealing with Murphy's Law and often make bets with each other over whether events will play out the way they're supposed to.

Zack often shares friendly banter with Melissa, occasionally exchanging jokes and pestering her as they go about their day. He tends to find Melissa's forgetfulness frustrating and often makes a monotonous comment when she forgets her belongings. He is also kissed on the cheek by her in "Sphere and Loathing in Outer Space".

The Lumberzacks
Before Zack moved to Danville, he and his former friends had formed a lumberjack-themed boy band. The five of them enjoyed their fame together until he ended up moving away, although the other members didn't seem too concerned about this. When he did see them again, the band's new leader, Max, provoked a rivalry between the now-renamed Lumbermaxes and Zack's new band, Just Getting Started. After the performance, they tried in vain to get Zack to rejoin.

Back when they were a band, they hung out together constantly, although they didn't seem to have the closest friendship. When a girl clearly cut in front of Max in a lineup, Zack went out of his way to claim that she wasn't in the wrong, starting a small argument with his bandmate over it. When he finally did leave the band, they barely looked up from their entertainment to say goodbye.

Max, as the voice of the group, doesn't seem to respect Zack much and tends to ignore his words in favor of hearing what he wants to hear, much to Zack's annoyance. He makes immature sounding assumptions that Zack is just using reverse psychology and secret messages to convey his actual thoughts.

Mort Schaeffer
Zack is on friendly terms with Mort. They are both players in the Jefferson County Middle School football team, and the two of them are a part of the band Just Getting Started. When Mort, like the others, was stressed out about their first live performance as a band, Zack reassured him it would be fine, managing to calm him down temporarily. And when Mort makes a bizarre comparison between Zack's past and a dance movie cliche, the latter excitedly agrees.

While trying to decide on a band name, Zack came up with 'The Sonic Three', unintentionally excluding Mort, much to his annoyance. Zack quickly apologizes and corrects himself, changing it to 'The Sonic Four' before naming a few others instead.

Amanda Lopez
Zack is on friendly terms with Amanda. Initially, he finds her obsession with order a little unusual, having recommended she switch to tangerine oranges to save time after finding out she had her entire day scheduled minute by minute. When he finds out that Milo was backstage to keep things from going wrong so that Amanda's enjoyment hours stayed safe, Zack joins him in trying to minimize the damage caused by Murphy's Law.

When she makes the announcement that she is their band's new manager, Zack questioned it, stating that he wasn't sure about having a manager before they even had a proper name. He was quick to accept her position, however, and obeyed all of her instructions when preparing for their concert.

Chad Van Coff\
Zack often seems amused by Chad's unusual antics, standing idly by while Melissa argues with him. When Chad made the suggestion that the punch was blood, Zack briefly pretended it was true to show how ridiculous that was. In spite of this, he was quick to go along with Chad's 'Vampire-hunter' theory and went out of his way to help him defend Mr. Drako.

Lydia
He and Lydia seem to get along. They have been practicing an interpretive dance for three weeks that they would do in "Ride Along Little Doggie", but Lydia got food poisoning and she was sick to do the dance. Zack was absent at the end of the episode, so he could have accompanied her with the paramedics to the hospital.

Martin and Brigette Murphy
Zack is on friendly terms with Milo's parents. When Brigette calls Melissa to ask her if they should invite Zack to the party, he informs her that he is fully insured, and even asks if they can make the party bigger. When he finds out that they'd accidentally donated Brigette's vintage T-shirt collection to charity, he works with Milo and Sara to get the shirts back as soon as possible. Zack is reasonably horrified when they return the shirts, only to find out that Brigette was planning on donating them anyway.

He tends to be a little nervous around Martin, knowing that the effects of Murphy's Law are multiplied when there is more than one Murphy in the area. He expressed this when he brings his own father on a fishing trip with Martin and Milo, and again when he voices his concerns about skiing with two Murphys. In spite of the extra danger, he enjoys hanging out with Milo's dad. Zack and Martin share a strong distaste for soy dogs.

Sara Murphy
Zack is on good terms with Milo's sister and enjoys hanging out with her. She spends quite a bit of time with the group, often ending up on adventures with them when things go out of hand. Sara, like Milo, was thrilled to catch him and Melissa up on Doctor Zone, although the latter two ended up more tired and confused about the show than excited. Afterward, while he seems to enjoy the show himself, he tends to find Sara's obsession with it odd. When she began to explain the costume she was making from an episode of Doctor Zone, Zack quickly stated that that was their cue before promptly leaving.

Zack hung out with Milo and Sara while they prepared some of Milo's clothing for donation. He claimed he didn't believe Sara when she repeated a conversation she'd had with her mother.

Balthazar Cavendish and Vinnie Dakota
Zack is on friendly terms with Cavendish and Dakota. Initially, he assumed, thanks to Chad, that the two of them were vampire hunters, which led to his confronting them at a school dance. This impression didn't last long, and eventually, they were formally introduced to him by Milo as time travelers. Afterward, he helped them save the world from the first Pistachion invasion.

During the second Pistachion invasion, Zack tells the others not to worry too much about stopping the invasion in their time period, reminding them that Cavendish and Dakota were back in the past, 'probably easily defeating the Pistachions'.

Having run into them after Murphy's law caused him to be late for school alongside Milo, Zack asks if Cavendish and Dakota would mind taking them back in time so that they can make their bell, only to find out that they were no longer allowed to time travel. In spite of this, they let him travel through time with Milo.

Scott
Zack is on good terms with Scott. While he's apprehensive of Scott's peculiarities, Zack is always happy to greet him. They'd originally met when Zack ended up underground with Milo and Melissa, and again after he'd been pursued underground with Melissa by Brick and Savannah. Scott helped him escape the agents and led him back up to the city.

While initially reluctant to help prepare Scott for a date, Zack joins his friends in a variety of activities before and during the date to keep things going as smoothly as possible. Like the others, he expresses disbelief over Scott's behavior.

Heinz Doofenshmirtz
Zack tends to be friendly towards Doofenshmirtz, but more often than not expresses disdain for his actions. When he was feeling claustro-avoidant in a museum exhibit, Zack was quick to take Doofenshmirtz' advice, holding his breath after he turns on an app for relaxation. He was so scared in Abducting Murphy Law because all of Doof Inators were after him and he even freaked out that he was turned inside out. Zach took a few interest in his inators like the Hand-to-foot inator.

Elliot Decker
Zack is often annoyed with Elliot for causing them trouble, and treats his antics with skepticism, calling him out whenever he tries to exaggerate his job. In spite of this, he tends to be friendly with the crossing guard.

Jackie
Zack had a brief crush on the danger-seeking girl, and he forced aside his typical cautious attitude to impress her. He was attracted to her for less than a day before he realized how dangerous she was.

Trivia

 * In "The Undergrounders", he appears to be claustrophobic, which is a fear of closed places; however, he says he's just 'claustro-avoidant'.
 * He states he has a fear of fish.
 * Though he has at least attempted to conquer his fear of fish that aren't in a body of water, he goes fishing in "Time Out".
 * His football jersey number is 19.
 * He can be considered a foil to Ferb. While Ferb doesn't talk much, Zack is often the voice of reason for Milo.
 * Like Ferb, Zack has separate voice actors for speaking and singing.
 * Zack being the voice of reason yet a best friend to the main character who is positive is similar to Gerald Johanssen from Hey Arnold! Dan Povenmire worked on Hey Arnold! prior to working on Milo Murphy's Law.
 * In "Fungus Among Us", he mentioned that he has at least two younger brothers who he claims can eat with their feet.
 * In "Love Toboggan", it was shown he knows how to snowboard.