Hyunckel is a central figure in the narrative of Dragon Quest: Dai no Daibōken, whose journey charts a course from bitter antagonist to steadfast hero. Orphaned as an infant when the Dark Lord Hadlar's armies razed his village, Hyunckel was discovered and adopted by Bartos, a powerful undead general serving the dark forces. Raised among monsters whom he came to regard as his true family, Hyunckel was instilled with a strong sense of honor and the warrior's code by his adoptive father. This upbringing would shape his entire worldview, creating a deep-seated loyalty to his monstrous kin and a profound estrangement from humanity. The pivotal tragedy of his youth occurred when the hero Avan successfully defeated Hadlar, an event that inadvertently led to the death of Bartos, killed by the resurrected and enraged Dark Lord. Hyunckel, unaware of the true circumstances, witnessed only the aftermath and came to believe that Avan was his father's murderer, setting him on a path of vengeance.

In his quest for retribution, Hyunckel sought out and became the first disciple of Avan, the very man he intended to kill. He concealed his burning hatred and secretly developed a lethal technique called Bloody Scryde for the purpose of assassination. However, Avan saw through the boy's facade and, when Hyunckel finally struck, he was able to deflect the attack, sending his vengeful student hurtling into a river. Following this failure, Hyunckel was taken in by Mystvearn, the shadowy twin of the Demon King Vearn, and rose through the ranks to become the formidable leader of the Undead Legion within the Dark Army. As the Dark Swordsman, he donned a suit of magical armor known as the Dark Armour Blade, summoned with the incantation Amdo, which was said to be capable of deflecting all attack magic. His appearance during this period is marked by silver and maroon armor with a skeletal visage, a flowing white cloak, and a helmet that only reveals his eyes, projecting an aura of menace and power.

Hyunckel's personality is defined by a powerful internal conflict between darkness and light, vengeance and honor. Consumed by a profound and misguided hatred for Avan and the ideals of justice he represents, Hyunckel is ruthless and coldly efficient in battle, showing little mercy to those he deems his enemies. He harbors a deep contempt for human sentiments and the symbol of Avan's teachings. Yet, despite his indomitable will to kill Avan, he is bound by the honor his father taught him, most notably his refusal to harm women, a principle he adheres to even at his most villainous. This creates a fascinating duality; he is a bitter young man driven by a vendetta, but his actions are governed by a strict, if twisted, personal code. After learning the truth about his father's death and defecting from the Dark Army, his personality undergoes a significant transformation. The hatred and resentment that once defined him are discarded, and he fully embraces his role as a disciple of Avan, fighting for justice and becoming a fiercely loyal and reliable ally.

Hyunckel's primary motivation is initially a singular, all-consuming desire for revenge against Avan for his father's perceived murder. This quest for vengeance is the engine that drives him to betray his master, join the demon army, and relentlessly pursue Dai and his friends. However, his role in the story shifts dramatically upon the revelation that it was actually Hadlar who murdered Bartos. This truth, delivered by Maam, shatters his entire worldview and removes the foundation of his hatred. His motivation then transforms into a path of redemption and atonement, as he seeks to right his past wrongs and honor the memory of his true father by fighting against the forces of evil he once served. He becomes a key member of Dai's party, using his immense strength and tactical brilliance to combat the Dark Army and protect the world.

His key relationships drive much of his character development. His connection to Bartos, his adoptive father, is the most significant, as his entire vendetta is rooted in love for the man who raised him and the monsters he saw as family. His relationship with Avan is complex, evolving from one of deceitful disciple and would-be assassin to a genuine, posthumous bond of master and student, as he later masters techniques that even Avan could not achieve. His initial antagonism with Dai gradually softens into a powerful alliance, with their battles and shared struggles forging a deep mutual respect. He also shares a unique bond with his former dark comrades; he possesses a grudging respect for honorable warriors like Crocodine, who ultimately saves his life and becomes a firm ally, and he despises the treacherous behavior of commanders like Flazzard and Zaboera. His mentorship under Mystvearn is fraught with tension, as he learns dark techniques like the Demon Puppetry Aura Hand but ultimately rejects his master's path.

Throughout the story, Hyunckel demonstrates remarkable development. He begins as a fearsome antagonist, the leader of the Undead Legion, whose power and dark charisma make him a formidable threat to the heroes. His defeat and subsequent rescue by Crocodine mark the beginning of his turn. The discovery of the truth about his father is the catalyst that allows him to shed his identity as the Dark Swordsman and embrace a new role as a champion of light. His development is further symbolized by his change in weaponry. After his Dark Armour Blade is destroyed, he receives the Dark Armour Spear, a weapon of equal power that forces him to adapt and master a new style, incorporating Avan's elemental techniques. His growth culminates in the creation of his ultimate technique, Grand Cross, a powerful cross-shaped attack that utilizes his entire life energy, representing his complete transition from a selfish avenger to a selfless hero willing to give everything for his companions and his cause.

Notable among Hyunckel's abilities is his mastery of swordsmanship and, later, spearmanship. As the leader of the Undead Legion, his signature equipment is the Dark Armour Blade, a demonic magic sword whose scabbard unravels to encase him in the ultra-durable Dark Armour. After losing this sword, he wields the equally powerful Dark Armour Spear. His techniques are fearsome, including the Bloody Scryde, a technique he invented to sacrifice his own blood to enhance his attack power. He is also proficient in the standard Avan Style techniques like Avan Strash. From Mystvearn, he learns the Demon Puppetry Aura Hand, a technique that allows him to control his own limbs remotely. His ultimate and most powerful ability is the Grand Cross, a technique that transforms his entire life force into a massive, devastating attack. Hyunckel is also known for his incredible resilience and fighting spirit, described by some as being nearly immortal due to his overwhelming willpower and ability to push past the brink of death to continue fighting.