The Underking The Underking is the name given to the undead form of either Zurin Arctus , the Imperial Battlemage of Emperor Tiber Septim , after his betrayal near the end of the Second Era ; or Ysmir Wulfharth , an ancient King of Skyrim who has lived many lives and was also betrayed by Tiber Septim . Although the Underking could very well contain a soul consisting of both individuals . Zurin Arctus . Zurin Arctus was a powerful mage , particularly within the school of Destruction . He was considered one of the best mages of his era , and authored a number of classic magical volumes ( see : " The Art of War Magic " ) . When Tiber Septim , who was then General Talos , became the " de - facto " leader of Cyrodiil , Arctus was a natural choice to serve as his Imperial Battlemage , for his superiority in Destruction made him a powerful Battlemage . Near the end of the Second Era , in the 9th century , Tiber Septim came into possession of a potent magical weapon : the Numidium . This giant golem was originally constructed by Kagrenac , the Dwemer high priest , in an attempt to lift his race above their own mortality . The golem had been in the possession of the Dunmer , specifically the Tribunal , since the defeat of the Dwemer and their disappearance from the province of Tamriel . Vivec made a deal with Septim ; in exchange for the use of Numidium , Morrowind would voluntarily join the Cyrodiilic Empire but be given a high degree of autonomy of government , much more than the other provinces had . Some sources claim that Arctus himself was directly responsible for obtaining the use of Numidium , and so became a powerful sorcerer not soon after . However , there was one problem with the Numidium that Tiber Septim needed to solve . The original plan was for the Dwemer to use the Heart of Lorkhan to power the device , thus granting Numidium god - like powers . The mere existence of the Heart of Lorkhan was one of the most closely guarded secrets in all of Tamriel . Even if Vivec had been willing to divulge the existence of the Heart , or its location under Red Mountain , it is unlikely that the Tribunal would have turned over the source of their divine power to the Imperials . Their immortality was not a bargainable thing with mortals of lesser power . Septim tasked Arctus with solving this problem , and the result was the creation of the Mantella , another powerful item . Arctus created the Mantella , a huge green gem , to house the required energy to power the device . Accounts from the time differ on exactly how the Mantella was filled ; the official Imperial histories claim that Septim himself gave his heart to create it ( thus , it is sometimes called the Heart of Tiber Septim ) . " The Arcturian Heresy " , described in more depth later , claims that the " real " Underking ' s soul was trapped by Arctus , killing them both in the struggle . Events surrounding the Numidium during the Third Era , in the Illiac Bay area of High Rock and Hammerfell , strongly suggest that it was Arctus , not Septim , who gave his heart to power the Mantella . It is unclear if this act was voluntary , though at least Mannimarco claims that Arctus was betrayed . In either case , if the Mantella was , in fact , the heart of Zurin Arctus , its loss did not kill him ; quite the opposite , his soul now refused to leave his body , and he lived on as the " Underking " and reaved the souls of others as a powerful Necromancer - like figure . The Underking . The Underking would proceed to cause problems for Septim for the remainder of his rule . His first major act was the destruction of the Numidium itself . By this time , according to some sources , Septim had been abusing the power of the Numidium against harmless , politically neutral parties . Arctus took offense at this , and smashed the golem to pieces , with the Totem being lost at the bottom of Illiac Bay , and the Mantella being sent to another plane of Aetherius for safe keeping . If Arctus was not already undead by this point , he undoubtedly was afterward . Years later , in 3E 36 , the Underking managed to infiltrate and corrupt the fortress of Sancre Tor . Previously , this site had been used as a tomb for the Reman line of Cyrodiilic kings , and Septim ' s Blades had set up a shrine to Septim containing his armor . The Underking sealed off the room containing Septim ' s armor , and populated the site with undead minions . Septim sent four of his Blades to the site to retrieve his armor , where they were trapped by the Underking and turned into undead guardians . After this , the Grandmaster of the Blades sealed the entrance to the tomb to prevent any further loss of life . After these events the Underking essentially vanished from Tamriel ' s history for hundreds of years . For the next approximately 400 years , no mention of him occurs in public record . Mannimarco , by this time also a powerful undead lich known as the King of Worms , does indicate that he had been in conflict with the Underking for centuries ; this leads to speculation that the Underking was , in fact , working for the good of the Empire after all . During the reign of Uriel Septim VII , both the Numidium and the Totem are found in the Illiac Bay region . This nearly set off a civil war amongst the dozens of independent city - states in the region , beginning with the murder of the King of Daggerfall . Ultimately , an anonymous hero traveled to the plane of Aetherius where the Mantella was located , and returned to Nirn with it to activate Numidium . As soon as the golem became active , the Underking arrived , destroyed the golem , retrieved his heart from the Mantella , and finally passed into true death . Once the Underking was gone , his hold over Sancre Tor diminished . The four undead Blades are finally laid to rest , after they collectively shatter the enchantment that imprisoned Septim ' s armor . Ysmir Wulfharth . A controversial , early historical account , " The Arcturian Heresy " , contradicts almost every accepted " fact " about the Underking and Zurin Arctus , claiming that Septim revised history upon taking the throne to protect himself and his reputation . The book identifies the Underking not as Zurin Arctus , but as King Wulfharth , an Atmoran who would become King Ysmir of the Nord s around 1E 500 . According to this account , after being defeated at Red Mountain , in the same battle that saw the disappearance of the Dwemer , Wulfharth returned to Skyrim and became Ysmir , driving out the Alessian religion from the Nords and reinstating their old gods . During the Second Akaviri Invasions , Ysmir also participated in driving back the Akaviri hordes . In this he is also mentioned as " the Underking " . He then waited for nearly three hundred years , until the Nord Greybeards began speaking of the rise of Talos , who would defeat the Nords ' ancient enemies , the mer , once and for all . The Underking worked his way into the role of advisor to General Talos , constantly urging him to invade Morrowind . Talos refused , choosing to concentrate first on the other human provinces such as Hammerfell . When Talos found the Numidium , however , and realized he would need a strong soul to power it , he tricked the Underking . His Battlemage , Zurin Arctus , trapped the Underking ' s soul in the Mantella , but not before the Underking managed to blast Arctus ' heart out and kill off Septim ' s guard . As he was the only one left alive , Septim now began to perpetuate the lie that Arctus betrayed his county , and tried to kill the Emperor ; and that , in retribution , his heart was trapped in the Mantella . As the Underking did not truly die , however , Septim needed to explain his existence , and claimed that Arctus himself was the undead lich , returned to take revenge for his death .