"Daoril is dead, burned away from the inside out. But we are beyond the door now. I have learned a valuable lesson from many foiled attempts: only a true nephalem shall possess the key to open it."— Korsikk in his journal(src)
Korsikk kept a journal during his early days. His father was obsessed with finding a hidden city of the nephalem, and Korsikk joined in the search. He found a location in mountains near Bramwell, which he believed was originally used as a shielded outpost for nephalem that were in danger. He stored a number of Zakarum artifacts in the cavern and had a Vizjerei Sorcerer trap a Bone Demon in it, to act as a guard until he returned. Korsikk believed that similar outposts existed all over Sanctuary. He believed that the city his father searched for was constructed by an ancient nephalem named Daedessa. The city was eventually found.
Korsikk succeeded his father as king of Westmarch, his father entombed in the nephalem city that had both searched for. After his coronation, his first official act was to present a special shield to the knight commander of the Knights of Westmarch.
He continued his father's task of turning the land into a bastion of the Zakarum faith. He also continued his father's wars against the northern tribes by constructing Bastion's Keep; the Bridge of Korsikk was apparently named after him. After years of military disasters, the frustrated king led a large army out of the fortress and into the north to conquer the Barbarians once and for all. None of them returned. With Korsikk's death, the location of the artifacts he'd hidden near Bramwell became lost.