As the firstborn son of King Jang Ryun and the queen, he became the crown prince of Seo Seo. However, when his father returned from a year-long inspection of the country with a commoner named Yeong Bi, his position was threatened lest the latter would give birth to a male son and become the crown prince favored by his father. As this did not happen, his title as crown prince was secured.
Together with his sisters, the First Prince would belittle and bully his half-sister Jang Rei, the daughter of Yeong Bi. The king favored the youngest the most due to her brilliant wit and intelligence, earning the jealousy of the First Prince and his siblings. Amidst this treatment, the prince also prohibited Rei to meet with his son Rok Ha, but the latter befriended Rei. Whenever he caught Rok Ha with Rei, he would frequently accuse Rei of beguiling his son with her looks, similar to how her mother "bewitched" their father. He continuously threatened Rei that he shall become king even if their father favored her over him and his siblings.
Following his father's death, the First Prince succeeded him and became king of Seo Seo. He found out about his father's will of having Rei inherit at least one-third of Seo Seo, much to his anger. His sister suggested getting rid of Rei and her mother, as she had already begun poisoning her tea gradually. As soon as Yeong Bi died, he sent Rok Ha abroad to study, leaving Rei with no ally nor friend.
During his reign, he continued the Ga Guk–Seo Seo peace treaty started by his father and King Jin Hyul. At some point, his health deteriorated, causing Rok Ha to persistently persuade him to step down from the throne. Eventually, he finally abdicated, with Rok Ha set to be coronated as the next ruler of Seo Seo.
When he was younger, he had shaggy long hair typically tied in a sangtu, sharp dark eyes, and prominent tear-troughs. He also had a very faint facial hair akin to a goatee. When he succeeded King Jang Ryun to the throne, he wore the myeonryugwan.
Like his sisters, he is slow-witted and greedy unlike his half-sister Rei, who was exceptionally intelligent. He is also straightforward with his thoughts and feelings to the point of using physical force to express his emotions, such as slapping Rei and blurting out that he shall become king after their father no matter how many times she complained to him (though Rei would actually keep her mouth shut regarding their pranks and humiliations).
|Characters of Twelve Nights|
|Royal Family||Ahn Young • Hyun Bin • Jin Hyul • Jin Jeok • Jin Won • Unnamed Baby Prince • Unnamed Baby Princess • Yi Hwi • Yi Sae Gi • Yoon Yeon Lee|
|Ministers||Hwang Se Hyung • Kim Hak Gyu • Sa Hwa Hyeon • Seo In Seon Woo • Wi Ji Hyun • Yi Ha • Yoo Ja Gyeom|
|Bi Yeong Pal Mu||Baek Ah • Baek Ju • Baek Lin • Baek Ryung • Baek Sa • Heuk Rang|
|Bi Yeong Ship Mu||Baek Ho • Baek Yoo Shin • Gil Mu Jin • Yi Ha|
|Deung Ha Bul Myung||Baek Ho • Crimson Moon • Gil Mu Jin • Nabi • Seol Hwa • Seo In Seon Woo • Wol Young Hwa • Yi Hwi • Yi Jeok|
|Yu Hyang Ru||Nabi • Wol Young Hwa • Yi Jeok|
|Others||Chung • Hwang Se Ryeon • Hyun • Ma Mi Song • Nam Yang Heon • Sori • Woon • Yi Ha's Wife • Yoo Dan Ah • Yoo Dan Ah's Mother|
|Royal Family||First Prince • First Princess • Jang Rei • Jang Rok Ha • Jang Ryun • Second Princess • Three Wives of Jang Ryun • Unnamed Baby Prince • Unnamed Baby Princess • Yeong Bi|
|Others||Gwak Ji Ryeon • Meng Gyeom|