This Article Contains Spoilers - WARNING: This article contains major spoilers. If you do not wish to know vital information on plot / character elements in a story, you may not wish to read beyond this warning: We hold no responsibility for any negative effects these facts may have on your enjoyment of said media should you continue. That is all.
Heiss is the hidden main antagonist of the Nintendo DS RPG Radiant Historia, being the primary antagonist in both of the game's timelines. He's in charge of Alistel Forces' Special Intelligence Division and is the superior of Stocke, the main protagonist.
Heiss was the unknown wielder of the Black Chronicle, forcing him to maintain a low profile and use the book to alter events in history to meet his desires. He was also manipulating in secret the heads of the continent's main cities: Alistel and Granorg; namely High Colonel Dias, Count Selvan, Queen Protea and General Hugo.
Heiss was the one to grant Stocke the enigmatic book, The White Chronicle, in hopes that he would find it useful. Which ultimately proved to be; as it, with the help of the Guardians of Historia, helped him travel through time in order to save countless lives, trump the conspiracies that were going on between both powers: Alistel and Granorg, and ultimately save the continent from the desertification. The Guardians' only condition was that Stocke kept the powers of the book a secret; they also warn him about the mysterious holder of the Black Chronicle, that is, the counterpart of the White Chronicle; someone who would try to halt his mission using the same time-traveling powers Stocke now had.
What the protagonist, his friends and even the opposing forces of the kingdom of Granorg don't know, is that Heiss is the wielder of the Black Chronicle and that he began utilizing its power even before the events of the game took place, altering history to meet his desires. Heiss was, in reality, the brother of the late King Victor from Granorg and was the next-in-line to take part in a sacrificial ritual used to stabilize Mana in the continent. Said ritual was necessary to avoid what everyone knew as the Sand Plague: fluctuating Mana escaping from living beings which resulted in them turning into sand. That ritual was to be carried out by the Royal Family of Granorg only; and, if done by a courageous one that fully understood them through History, Mana was stabilized for many generations to come.
Heiss did not want to partake in the ritual and with the aid of the Black Chronicle, he only saw futility in sacrificing a good man for the sake of a selfish, vain place. He kidnapped the fair prince Ernst and fled Granorg. There, he used the Black Chronicle and turned his nephew into someone he could use in the future, he named him Stocke. He also altered history to finish off Raini and Marco's brigade so they could be assigned to Specint with Stocke. Heiss' ultimate goal was for the world to end, having lost all faith in it.
Near the end of the game; The Guardians of Historia, Lippti and Teo, reveal Stocke that all of the White Chronicle wielders have been sacrifices from the Royal Family and the White Chronicle helps them "gain character", while all the members of the Black Chronicle only see despair in the world and are bound by the tragedies of the past. They also warn him that Heiss has become too powerful, even for them, but they still have to avail by the rules of Historia. Still, they hint him about what's Heiss plans are and where he has gone off to to assasinate Princess Eruca, Stocke's sister. By breaking the rules, Lippti and Teo were painfully punished, so Stocke stops them before they say anything else and thanks them for their help. He faces Heiss in the Gran Plain and is defeated. The wielder of the Black Chronicle finally decides to stand up to Stocke and appoints him in the Chamber of Flux for the final battle. Before the event, he sacrifices Dias and Selvan to Flux and gains even more power. Stocke and his friends face off against all the powers of the Black Chronicle and multiple versions of Heiss from the Multiverse. The Black Chronicle is defeated and the antagonist recurs to using the powers of the Black Chronicle wielders past and takes the battle to Historia. Thanks to this, Heiss transforms into Historia's antithesis, Apocrypha. After the hardest battle yet, Stocke and his friends defeat it and Heiss crumbles away.