Harkon once ruled as a mighty king. His domain was said to be vast and powerful. His greatest fear was his own mortality, so he pledged himself to Molag Bal and in his name he sacrificed a thousand innocents. In return, Molag Bal granted him immortality by turning him and his family into pure-blood vampires.
As the years passed, he uncovered a prophecy called the Tyranny of the Sun, that, if enacted, would blot out the sun and allow his kin to roam freely during the day. He became obsessed with the prophecy and everything in his life, including his family, was pushed aside.
To enact the prophecy he required the ancient artifact called Auriel's Bow and the blood of a Daughter of Coldharbour, namely his daughter, Serana. His estranged wife Valerica saw the change in Harkon's behavior and disagreed with his goal. She believed that vampires should stay in the shadows otherwise it would bring too much attention and ultimately lead to their extinction.
In an attempt to stop him fulfilling the prophecy, she locked Serana and one Elder Scroll in Dimhollow Crypt for her protection and escaped to the Soul Cairn with the other sometime in the First Era. Harkon, enraged by this betrayal, commanded every vampire in his court to look for them, but after centuries of searching, he lost hope.
Harkon is an elitist, and sees mortals as inferior beings. He has little regard even for his family, and only remembers his wife and daughter due to his lust for power. Harkon is cruel and will not let anything stop him in his quest for domination. He views the vampires found throughout the rest of Skyrim to be no more than feral animals that "frighten the herd" of mortal citizens of Skyrim that he and his fellow "pure-bloods" feed upon.
He harbors significant resentment towards his estranged wife, Valerica, and wished to enact revenge upon her for her betrayal. Similarly, Harkon holds a deep abhorrence for lycanthropes, considering the condition "filthy".
The Dragonborn first encounters Harkon upon returning Serana to Castle Volkihar in the quest Dawnguard. As a reward, he offers the Dragonborn the ability to become a Vampire Lord and take sides with the vampires. Alternatively, the Dragonborn can refuse his offer and join the campaign against him, with the Dawnguard.
If the Dragonborn sides with the vampires, Harkon sends the Dragonborn and Serana on a quest to find someone capable of reading the Elder Scroll. After learning that two additional Scrolls are needed to complete the prophecy, he sends the Dragonborn to find them, stating that they are located hidden with his wife Valerica and in some Dwarven ruins. After finding and deciphering the last two Elder Scrolls, the Dragonborn is finally sent to recover Auriel's Bow.Elder Scrolls of Blood, Dragon and Sun have been deciphered and Auriel's Bow been gained in the quest Touching the Sky, the Dragonborn and Serana goes to Castle Volkihar to confront Harkon in the quest Kindred Judgment. After some dialogue, there is the option to either kill Harkon or give him the bow. Either way, Harkon begins the fight.
- Harkon's Sword
- Potion of Blood
- Vampire Royal Armor
- Vampire Boots
- Random enchanted or unenchanted jewelry
- One of many assorted random potions
- "You have forsaken my gift. The ancient blood no longer flows through your veins. Don't deny it!. Count yourself fortunate that I'm a forgiving man. Now, be still while I give you the ancient blood once again." - If cured of Vampirism.
- "I see you have my Elder Scroll."
- Despite Serana and Valerica being Vampire Lords as well, Harkon is the only one to take the form in battle.
- If the Dragonborn is a werewolf, Harkon will have additional dialogue during their first conversation, noticing their "smell".
- If the Dragonborn has contracted with Sanguine Vampiris, he will say that they only contracted with the disease and are not a true Vampire.
- Before the final fight, he will say "This Dragon has fangs", referring how the Dragonborn managed to convince Serana to turn her against him. This also would mean that he knows that the player character is a Dragonborn.