Cpt. Yoo Si-jin
The Leader of Alpha Squad, a team under the South Korean special forces. Although he and Mo-yeon are easily attracted to each other when they meet in Korea, they have trouble with the secrecy Si-jin's job entails. Si-jin becomes The Captain of a peacekeeping squadron in Uruk. Si-jin is friendly, charismatic, and cool under fire, but has difficulty being honest with Mo-yeon. His callsign is "Big Boss."
- Bad Liar: He and Dae-young are utterly incapable of keeping their stories straight.
- The Captain: He's the leader of Alpha Squad, as well as the Moworu Power Plant peacekeeping team. Thus, he's usually the one taking responsibility for the goings-on within the camp.
- Captain Smooth and Sergeant Rough: The Captain Smooth to Dae-young's Sergeant Rough. Si-jin is more charismatic and is usually the one dealing with the highers-up and giving orders.
- Dogged Nice Guy: His relentless pursuit of Mo-yeon even as she tries to avoid him in the early episodes can come off as this.
- Good-Looking PrivatesEun-ji: Who knew a soldier could be so handsome!
- The Hero: Much of the action is his escapades as a member of the special forces.
- Manly Tears:
- When he's forced to kill Argus, and in the aftermath he cries again when burning their picture together.
- When he is reunited with Mo-yeon in Albania a year after his supposed death anniversary.
- Military Maverick: He isn't afraid to go against orders if the orders compromise his principles (such as knowingly endangering other people). Good thing he's competent enough to pull it off.
- My Country, Right or Wrong: Played with. Si-jin is intensely loyal to his country and its safety is his primary priority and reason for fighting, but he is willing to go against official orders by highers-up if they contradict his principles.
- No One Gets Left Behind: He won't leave a man behind if he can help it. In the past, he went through enemy fire in order to rescue then-Captain Argus.
- We Used to Be Friends: Si-jin can't believe that Argus, the man who Si-jin rescued under enemy fire, is now the Big Bad.
Dr. Kang Mo-yeon
A civilian surgeon at Haesung Hospital. Mo-yeon begins the series attempting to advance to a professor position, but continually fails because Hard Work Hardly Works. When she spurns the advances of the hospital chairman, he sends her to lead a volunteer mission in Uruk. Mo-yeon is down-to-earth and level-headed, but struggles with the dangers of Si-jin's job.
- Adorkable: She's excitable, cheery, and endearingly awkward in the face of romance.
- Big Sister Mentor: To Fatima; she encourages her to continue her studies despite the traumatic things that happened to her. By the end of the series, Fatima affirms her desire to be a doctor like Mo-yeon.
- Distressed Damsel: She's kidnapped by Argus and used as bait so Si-jin will secure him an escape route.
- The Face: She becomes this for Haesung Hospital in the eight-month skip between episodes 1 and 2, appearing in several medical ads for the hospital. She's also this for the medical mission team, as the lead doctor.
- Got Volunteered: To lead the medical mission in Uruk by the hospital director, who was angry that she rejected him.
- Hard Work Hardly Works: Discussed. She's passed over for a professor position three times; the third was because her incompetent competition was wealthy and well-connected within the hospital. Despite how competent she is as a surgeon, she won't advance because she doesn't have connections.
- Hospital Hottie: Other characters note how pretty she is.
- Nice Girl: She's undeniably a kind, well-adjusted, intelligent woman who genuinely cares for other people.
- Reality Ensues: Her awesome moment of throwing her resignation in Director Han's face and opening up a clinic in Gangnam backfires when she realizes she can't get a loan without a job.
- Tsundere: Her harsh avoidance of Si-jin failed to hide her genuine interest in him, and she warms up soon enough.
- Workaholic: As noted by the other characters, she practically lives in the on-call and the operating rooms.
Sgt. Maj. Seo Dae-young
Si-jin's best friend, trusted second-in-command, and a trainer at the military academy. Although not as easy-going as Si-jin, Dae-young shares his drive, bravery, and loyalty. He has requited feelings for Myeung-joo, but his adherence to the rules and his respect for Myeung-joo's father hamper their relationship. His callsign is "Wolf."
- Bad Liar: Exceedingly so.Dae-young: I'm dating Lieutenant Yoon Myeung-joo.
Si-jin: And how long have you been seeing each other?
Dae-young': It's been a year.
Si-jin: When did you first see Myeung-joo?
Dae-young: I met her a month ago at the thousand-mile march.
Si-jin: But you've been going out for a year?!
- The Beard: He and Myeung-joo were this to each other in their backstory; she pretended to be his date to his ex-girlfriend's wedding if he would pretend to be her boyfriend so Si-jin wouldn't pursue her at her father's pressing. It developed into a real relationship from there.
- Big Brother Mentor: To Kim Gi Beom, whom he bails out of trouble in the first episode. When we see Gi Beom next, he's shaped up thanks to his military training and clearly looks up to Dae-young.
- Break Her Heart to Save Her: Initially breaks it off with Myeung-joo at the request of her father, who believes that he will not provide her with a good future.
- Captain Smooth and Sergeant Rough: The Sergeant Rough to Si-jin's Captain Smooth. Dae-young is less outspoken and is more concerned with enforcing orders and making sure everything is in place.
- Career Versus Man: Rare Male Example. Lt. Gen. Yoon presents him with a choice: get to date Myeung-joo but leave the army, or stay in the army without her.
- The Comically Serious: His stoicism is occasionally played for laughs, such as in the first episode where Kim Gi Beom steals his phone.
- Drill Sergeant Nasty: He actually is a drill sergeant, and thus handles his trainees with the harshness one would expect.
- Manly Tears: When Myeung-joo is diagnosed with a virus, and when he's reunited with her in Uruk after a year of being presumed dead.
- Not So Stoic: His blankness tends to break whenever Myeung-joo is concerned.
- Number Two: To Si-jin; he follows through with Si-jin's orders without fail.
- The Stoic: He has an impressive poker face on most of the time, in contrast to Si-jin, who takes great pleasure in poking fun at him. This is more pronounced in the past; in later episodes he emotes more freely due to the other characters' influence.
Lt. Yoon Myeung-joo
An army surgeon ranked lieutenant and colleague of Si-jin and Dae-young. She and Dae-young have feelings for each other, but their relationship is hampered by Myeung-joo's high-ranking father. There is also tension between her and Mo-yeon stemming from when Myeung-joo interned at Haesung; allegedly, Myeung-joo went out with Mo-yeon's crush.
- The Beard: To Dae-young in their backstory; she was his date to his ex's wedding in return for him pretending to be her boyfriend in front of Si-jin.
- Combat Medic: As an army surgeon, it comes with the territory.
- Daddy's Girl: She loves her father and is close to him, despite their relationship in the present being strained.
- The General's Daughter: Her father disapproves of her relationship with Dae-young because he's ranked lower than she is.
- Good-Looking Privates: She's noted to be pretty.
- Military Brat: Her father is a high-ranking officer (specifically the commander of Special Forces). She followed in his footsteps and joined the army.
- Ill Girl: Myeung-joo gets a subplot where she catches an Ebola-like virus, and is thus otherwise indisposed in the Medicube as her illness worsens. She gets better.
- Just Friends: With Si-jin, despite her father insisting that Si-jin would make a better son-in-law than Dae-young. Mo-yeon is quick to question this.
- Playing Gertrude: Kim Ji-Won was 22 during production, playing a relatively experienced soldier of an age with the other main charactersnote .
- The Squadette: During her dispatch to Uruk, she's the only female soldier seen with the Moworu squadron.
- Tsundere: Towards Dae-young, in early episodes. She'd act harsh with him and hit him before showing a softer side; justified in that it's on the tail end of their not-so-smooth separation/breakup and Dae-young refuses to respond to her.
The son of a rich family and a first-year resident who joins the volunteer team, leaving behind his pregnant fiancee. Chi-hoon is earnest and well-meaning but is also inexperienced and naive.
- Break the Cutie: When he abandons a patient in the rubble of the destroyed power plant out of fear and inexperience, the experience haunts him for several weeks. He's finally able to come to terms with it after the patient he left behind gives him his approval.
- The Dandy: Cares about grooming and fashion moreso than the other hospital volunteers; his Break the Cutie stint is noted by, among other things, wearing the same shoes for three days straight.
A general surgeon who provides experience to the volunteer team despite his eccentricities. He relentlessly flirts with Ja-ae.
- Bunny-Ears Lawyer: In the words of Ja-ae, he's a useless guy but a good doctor.
- Childhood Friend Romance: He and Ja-ae have been friends since at least their teens, and get together in the end.
An ER nurse who tends to serve as the Voice of Reason. She joins the volunteer mission to Uruk. She is longtime friends with Sang-hyun.
- Childhood Friend Romance: She and Sang-hyun have been friends since at least their teens, and get together in the end.
- Tsundere: She pretends to not care about Sang-hyun, but worries about him when he comes down with a cold.
- Voice of Reason: She balances out Sang-hyun's eccentricities, Chi-hoon and Min-ji's youth and inexperience, and Mo-yeon's drama. She's not above Eating the Eye Candy, though.
- The Cutie: Remains fresh-faced, adorable, and innocent.
- Flat Character: She's not given as much in the way of characterization or subplot as the other characters.
The director of Haesung Hospital.
- Abhorrent Admirer: To Mo-yeon.
- Crazy Jealous Guy: Over Mo-yeon; once she comes back from Uruk with a handsome boyfriend he reacts extremely negatively.
- Disproportionate Retribution: His reaction to Mo-yeon rejecting his advances and hitting him with her bag? Send her on a volunteer mission all the way around the globe.
The remaining members of Alpha Team, who run missions with Si-jin and Dae-young. Their names are Sgt. Choi Woo-geun (callsign "Snoopy"), SSgt. Gong Cheol-ho (callsign "Harry Potter") and Sgt. Im Gwang-nam (callsign "Piccolo").
- Demolitions Expert: Choi is one; he's the one who removes the time bomb vest Mo-yeon is forced to wear during her kidnapping.
- Those Two Guys: Choi is the next most prominent Alpha Team member, Gong and Im exist mostly to fill in the ranks.
- The Squad
- True Companions: Comes with being a team of special forces agents who've known each other for years.
Lt. Gen. Yoon Gil Joon
Myeung-ju's father and commander of the Special Forces.
- Papa Wolf: His daughter's safety and future is his primary priority.
- Reasonable Authority Figure: What he strives to be; he's willing to take responsibility for Si-jin and the rest of Alpha Team rescuing Mo-yeon from Argus. He's just really against the idea of his daughter dating Dae-young.
- Shipping Torpedo: The primary obstacle between Dae-young and Myeung-joo. He prefers her with Si-jin, who seems to find the entire ordeal amusing.
L.Cpl. Kim Gi-beom
A petty criminal Si-jin and Dae-young bail out of trouble in the first episode. He undergoes his mandatory military service soon after.
- Reformed Criminal: He was a petty pickpocket and gang member before joining the military. By the series' end, he's a platoon sergeant.
- Team Chef: He's a surprisingly good cook, and is the one making the meals for the cast while they're in Uruk.
A former Special Forces operative turned illegal arms dealer.
- Arms Dealer: His current occupation is dealing illegal weapons. In fact, it's the reason he hasn't been dealt with yet despite being ex-military — the US wants him to sell weapons to a pro-American faction planning to stage a coup. He's aware of this, though, and takes measures to secure an escape route.
- Big Bad Friend: To Si-jin, who once partook in a mission to rescue him.
- Faux Affably Evil: He's affable and polite but doesn't pretend to be a nice guy; he'll pretend to make small talk while hitting you across the face.
- Man of Wealth and Taste: He's always seen in a suit.
- Multiple Gunshot Death: How he eventually goes, courtesy of Si-jin.
- Would Hurt a Child: Argus's gang is also involved in child trafficking.
- You Have Failed Me: He's not afraid to shoot henchmen who disappoint him dead.
A doctor who works with several volunteer organizations.
- Hospital Hottie: A licensed medical professional with several characters acknowledging his attractiveness.
- Mixed Ancestry: Half-Korean, half-Canadian.
- Mr. Fixit: As Si-jin put it, there's nothing Daniel can't fix — demonstrated when he revives a car Mo-yeon had previously driven off a cliff and into the ocean.
- Spoiled Sweet: Lampshaded by the cast. His father is immensely wealthy, but he spends his time working with do-gooder organizations.
Daniel's partner, who works as a nurse using Oriental medicine.
- Back-Alley Doctor: Of a sorts; she doesn't have a medical license and instead performs Oriental medicine.
- He Is Not My Boyfriend: She denies any romantic liaisons between her and Daniel when questioned, claiming them to be just co-owners. They're married by the series' end.
The general manager of the Moworu plant.
- Jerkass: His attitude in the aftermath of the earthquake, demanding that the soldiers focus their rescue operations on the office containing the diamonds Argus was demanding despite how illogical it was logistically.
- Stomach of Holding: He swallows Argus's diamonds to keep them away from him twice. Deconstructed, as the second time gets him severely ill and hospitalized.
A young girl who gets caught up in Argus's dealings.
- Dark-Skinned Blonde: She has tanned skin and blonde hair.