Hak (ハク Haku?) is the tritagonist of the manga and anime series, Akatsuki no Yona. He is formerly known as Son Hak (ソン ハク Son Haku?), the former General and Chief of the Wind Tribe. He is an adopted grandson of Son Mundok, the adoptive brother of Tae-Yeon, and the childhood friend of Princess Yona and Soo-Won. Throughout the Kingdom of Kouka, he is known as the "Lightning Beast" due to his outstanding martial arts skills, gaining fame as one of the strongest fighters in the country.
Sarcastic, nonchalant, and often found teasing the Princess, he was appointed as her bodyguard by Emperor Il at the age of 15. Despite having feelings for her from a young age, Hak's goal in life was to become the right-hand man of his best friend, Soo-Won, once he became the next king of Kouka, and he had resolved himself to serving both of his childhood friends for the rest his life. However, after Soo-Won's betrayal, Hak was forced to save Yona from imminent death, and bring her to the Wind Tribe for her safety. Falsely rumored to be the murderer of Il and to have kidnapped Yona, he attempted to leave the Wind Tribe as a fugitive, but after Yona's persuasion, decided to go along with her as she travelled to find the 4 dragons to protect them.
Being a deeply loyal and straight-forward person, he was severely hurt by his best friend Soo-Won's betrayal and has arguably had a harder time coming to terms with it than Yona. Originally extremely overprotective of Yona, he later grows out of it when he sees her determination to become stronger and begins taking pride in her fiery side. Along the way he started to make new friendships within the group and learning that he's not alone in the fight to protect Yona.
Hak is described as a tall, tough-bodied, and attractive young man with sharp blue eyes, broad shoulders and with a six pack. He has short messy black hair with bangs hanging below his eyes. He has a well-built frame cultivated from years of training, which tends to make him quite popular with girls. He wears a sleeveless blue overcoat seamed with bluish-black hemlines over a royal blue robe with black collar and sash. He ties black ribbons in a crisscross pattern over the lower half of his sleeves to prevent them from getting in the way when he is fighting. Underneath his robe, he wears black pants and a pair of dark brown boots overlaid with more crisscross-patterned ribbons. Occasionally, he can be seen wearing a sled hat when he is hiding his identity.
He always (apart from sometimes when in disguise) carries his signature weapon, a Chinese glaive-like weapon called a Hsu Quandao, most of the time with its blade draped in a white cloth held by a black strap. Underneath his garments he always wears the Lapis Lazuli necklace Yona gifted him which can be seen in the manga numerous times.
Hak is a sarcastic, straight-forward young man who strives to protect Yona at all costs. He is self-sacrificing, both physically and emotionally, when it comes to her well being, as well as incredibly loyal to those he respects and obeys. Hak has been shown to have a mischievous streak as well, often teasing Yona and the others of his party, as well as a "having a habit" of being a bully who enjoys branding some of their other companions with mocking nicknames, like "White Snake" (Kija) and "Droopy Eyes" (Jae-Ha). Despite this, he is serious whenever it comes to his job. His professionalism extends to a point where he even addresses his childhood friends formally by their status. His devotion to his job stems from his belief in Emperor Il. At first, he had no intention of getting involved with the royal family, as he saw it as troublesome. However, when he witnessed the emperor’s bravery one day, he swore loyalty to them.
Hak, being a naturally loyal person, was the angriest at Soo-won's betrayal. Hak was willing to put aside his feelings for Yona, even if it was painful, so that she could marry Soo-Won. He would have happily served under them for the rest of their lives, so they could all remain friends. The fact that Soo-Won was willing to kill Yona, the person Hak loves most, and destroy her entire future for the throne broke Hak's heart. On the very day Soo-Won killed King Il, he gave Yona a hairpin and told her her hair was beautiful (knowing that she hated her hair at the time). She had just confessed her feelings for Soo-Won and Hak thought him unforgivably cruel for doing that to her.
In the recent chapters of the manga, Hak for the first time had a monologue where he talks about his feeling towards Soo-Won. It is clear that Hak struggles with feelings of intense betrayal and grieves for the relationship they once had. He still doesn't understand why the current king of Kouka had to kill King Il to get power. Hak idolized and respected Soo-Won. Their relationship was like that of brothers. Soo-Won's betrayal made it difficult for Hak to trust anyone with protecting Yona, even the four dragons. As time passed, he began to open up again and now cares deeply for his teammates. Out of the four dragons, he is closest with Jae-ha (speaking frankly with him often) and Kija despite their different personalities and banter they have seemed to care about one another and will protect each other and their teammates. Hak is also shown to deeply trust Yoon and be protective of him.
When it comes to his feelings for Yona, Hak destroys his impulses every time they surface, even though it hurts to do so. There are times that he will show his affection with teasing, but not much beyond that. However, when someone (usually Jae-Ha) questions the emotional distance between Hak and Yona, Hak loses his composure and can become territorial around the princess. He seems cold around Yona at first but slowly reveals that he cares deeply for her. Hak has been in love with Yona since childhood, but never confessed out of respect for her feelings towards Soo-Won. Because of that, he's had more of a brother-sister relationship with her. Hak gave up his General title and his livelihood in the Wind Tribe to keep her safe which shows his loyalty, integrity, and devotion to not only Yona but to King Il as well.
Hak, in general, isn't a forgiving person and that is why he finds it so hard to understand people like Yona and Jae-Ha who choose not to be swallowed by the impulse for revenge and move past the hardships they have faced in life. Hak wants to be able to do the same. In Chapter 147, as he rescued Jae-Ha and Kija from the Xing soldiers he mentally asks Yona and Jae-Ha how he can move to past his hatred for others that are trying to hurt them and for Soo-Won in particular. Although Hak has gained better control over his emotions when it comes to seeing Soo-Won face to face, he, like Yona, still suffers from the emotional and mental trauma of the betrayal. In chapter 178, when Keishuk asks them to return to the castle and form an alliance, Hak becomes emotional and tells Yona he will never forgive Soo-Won after everything he's done.
Hak was adopted by Mundok at age 2, after losing his parents in the original Xing war. Mundok acted as a surrogate grandfather and Hak gained many friends/surrogate siblings under his care. Hak was well liked by the children he grew up with and was considered a big brother to many. Under Mundok's guidance, he became one of the strongest members of the Wind Tribe. At about 6 years old Hak wandered off while Mundok was at a Five Tribes meeting and began playing with Soo-won in the castle gardens. Soo-won was amazed by Hak's speed while scaling a tree - Soo-won introduced Hak to a small Yona and the three played happily together. Hak initially thought that Yona hated him but Soo-won assured him that she was shy with strangers. That day, Hak met both of their mothers - while Kashi rushed to stop Hak as he tugged Yona away to play, she paused as he turned towards her and instead instructed him to "protect Yona". With Kashi having been able to see the futures of others, it is possible she foresaw how significant Hak would be in Yona's life.
By the age of thirteen, he was powerful enough to defeat Lee Geun-Tae who was already a general at that time. At fifteen, he became Mundok’s successor and Yona’s exclusive bodyguard (the Sky Tribe General snubbed for the position). Initially, he was against the idea of being a servant, telling Emperor Il that he wouldn’t be able to take afternoon naps if he were to accept the task. He also deemed the job impossible to be done, due to the emperor’s dislike of weapons. However, when Yona was being harassed by Kan Tae-Jun, he stopped him and finally accepted the position Emperor Il offered. When he reached fifteen he became the General Commander at the castle. Added to his list of titles is 'Chief of the Wind Tribe' which makes him one very young and accomplished person.
At the age of Eighteen, Hak is considered by many to be the greatest Koukan warrior ever to grace a battlefield to the point where even the dragon warriors can agree to this as he can keep up with them in battle and fight them head-on.
- Martial Skills: Hak's skills with the Chinese Guandao polearm, or glaive, are the best in the country. His speed and strength allow him to deal with powerful blows, even sweeping aside a large area of fog with one swift stroke.
- Swordsmanship: While not his first choice of weapon, Hak is proficient with a sword and ultimately is the one who trains Yona in swordsmanship.
- Archery: Hak is an excellent shot with a bow, able to shoot bullseyes and birds out out the sky with ease, even on horseback. He is also the person who mostly teaches Yona archery, though Yoon also contributes.
- Immense Strength: He is noted to have unusual strength by numerous people, including the four dragon warriors. Even without his weapon, he can deal with strong blows with his fists. Due to his strength and abilities, he was jokingly given the name "Black Dragon", or "Darkness Dragon" by Kija. Despite this, Hak soon was considered as the fifth dragon by the other four dragons. Although not a dragon-blooded warrior, he matches the strength of other dragons easily. His strength in battle was equal and often exceeded that of The Five Stars (him sparring with Algira, their strongest fighter), the best warriors of the Xing kingdom. Hak is strong enough to catch boulders while sitting comfortably with one hand.
- Endurance: One of his more defining attributes is his stalwart heartiness, first shown when enduring a bite from a venomous snake when protecting Yona. That being said, this may be mostly due to his determination to live and protect Yona.
- Basic Medical Skills: Though not as good as Yoon, Hak has shown to have a basic knowledge of medicine. He was able to remove snake poison from his system, and he shows Yona how to remove the thorns and disinfect the cuts she received from the Senjuso test.
- Charisma: Wherever Hak goes he reaches people's hearts and makes them want to follow him. Yona said "Hak does draw in all kinds of people. That's how it always have been."
- Political and military knowledge: Hak is able to read military situations and understands political schemes.
- [source needed] "A world without weaponry and war, where no one gets hurt, is but a pipe dream." 
- (To Yona) "Keep your mouth shut and hang on, Princess. I don't care what I have to do. His Majesty is gone now. My master is you. Think of me as a tool. Use me so that you can live! That's what I'm here for!" 
- (To Yona) "Don't interfere. Before we met you, she did this all the time. When she has enough time, she shoots off as much as 200 arrows in one night. Because I'm here, she doesn't have to do anything. But the princess won't allow herself to be powerless. Her father was killed, and she escaped from the castle. She does this to survive in this world. She's doing whatever she must do. It's not necessarily that I want her to be able to fight, but... I think I also want to see her struggle like a human being." 
- (To himself about Soo-Won) "Amazing... one word from Soo-Won makes the whole town move." 
- (To himself about Soo-Won) "He is a noble. He can also move many different kinds of people. He’s an amazing guy with tons of power… someone like him is looking at me. I need to become someone worthy of your goal. So that from now on, we can walk as equals." 
- (To Soo-Won) "I felt that you were a guy with such a broad outlook. Differences in position or tribe didn’t matter. You were able to see the world with fair, impartial eyes. In the future, even if I would no longer be able to walk beside you as your equal, that would be fine. Without looking back, only looking forward, I… wanted for you to be King. And then my dream came true in the worst form imaginable." 
- (To Soo-Won) "This guy genuinely, seriously, might like all people. No, not just all people, all things. And he is interested in them all equally. There are a lot of people I don’t really like, and a lot of things I can’t stand, but… you were looking much further ahead, weren’t you?" 
- (To Yona) "I'm immortal. Actually, I can't afford to die. I've got a troublesome princess to look after." 
- (To Yoon) "When you protect someone you want to keep safe, do you always weigh your own life against theirs?" 
- [source needed] "When I'm around the princess, I lose my mind." 
- (To Jae-Ha) "I don't swing that way pal." 
- (To Yona) "I've willingly followed you. I've been overwhelmed by your strength and passion. I want to devote my life to you. You're the one who taught me the pride of serving someone!" 
- In the planning phase of Akatsuki no Yona, Hak’s original name was “Soron”. It seemed too similar to “Soo-won”, so it was changed to “Hak-jin”. In the end, it was shortened to “Hak”. The name "Soron" was later re-used as the name of Mundok's deceased biological son.
- Alongside Soo-won, he helped train the hawk Gulfan which is in Soo-won's possession. The bird is shown to descend for (recognising him as a master) and be affectionate towards him.
- He ranked 1st in the character popularity poll conducted by Hana to Yume in December 2014. He scored 3,001 votes in total.
- According to the 2018 Akatsuki no Yona Fanbook, his parents were casualties of war 16 years ago. He was orphaned at age 2, around the time Yona was born.
- Hak often refers to himself as the fifth "Darkness" Dragon, in reference to a joke made by Kija that he would be an evil "Darkness Dragon" if he were to be one of the dragons.
- Hak is considered the strongest warriors in the kingdom. Even some of the dragon warriors are intimidated by his ferocity in battle. For example, Kija thought that Hak's strength could match the strength of his Dragon's hand, and Jae-Ha also believes Hak is very strong.
- According to Kusanagi, she stated in a side note in Vol. 27 that Hak acted like an older brother to the members of The Wind Tribe. But after meeting Kija and Jae-Ha, Hak now sees them as older brothers and can feel bit vulnerable around them even though he will never admit it.
- Akatsuki no Yona Chapter 43, Page 7
- Akatsuki no Yona Volume 17
- Kusanagi Mizuho's Twitter
- Akatsuki no Yona Chapter 15, Page 2
- Akatsuki no Yona Chapter 01, Page 56
- Akatsuki no Yona Chapter 03, Pages 27-28
- Akatsuki no Yona Chapter 32, Pages 30-33
- Akatsuki no Yona Fanbook
- Akatsuki no Yona Chapter 03, Pages 26-28
- Akatsuki no Yona Chapter 18, Page 20
- Akatsuki no Yona Chapter 42, Page 22
- Akatsuki no Yona Chapter 152, Page 29
- Akatsuki no Yona Chapter 152, Page 29
- Hana to Yume (花とゆめ), 2015/1 edition