Cho Beom-il was a commander in the Royal Army of Joseon. He was a member of the Haewon Cho clan and the the son of the powerful Chief State Councilor Cho Hak-ju. Lord Cho entrusted him with securing his interests in the capital and rooting out the clan's enemies. He was also involved in his father's plot to resurrect the King and keep him alive until the Queen had given birth to a son. He is one of the overarching antagonist of the series .
When the Crown Prince escaped after being accused of treason, Lord Cho sent his son and several soldiers and bring him back. Beom-il successfully tracked the crown prince to the Jiyulheon clinic near Dongnae. After reading him the warrant for his arrest, they engaged in a short sword fight, with Beom-il emerging victorious. Unfortunately for him, the clinic had been overtaken by an outbreak of the King's strange illness, and they are attacked by its former head, Lee Seung-hui, who has become infected. Lee infects one of Beom-il's guards, who in turn infects Beom-il, and the Crown Prince is ultimately forced to kill him.
When Lord Cho receives his son's head from the surviving guard, he swears revenge on the Crown Prince and his followers.
In Ashin of the North, it was revealed that Beom-il and his men were responsible for the killings of the innocent Pajeowi Jurchens at the Pyesagun forest due to the allegation of them stealing precious wild ginsengs from his clan. His action paves way to Ashin's quest for vengeance against the Joseon Kingdom and the entire event of the series.