|“||There must always be... a Lich King.||„|
|~ Each hero, once they transform into a Death Knight.|
The Death Knights are the corrupted death knight versions of the nine original heroes of Hearthstone, appearing in the Knights of the Frozen Throne expansion. Before their corruption, they all fought their way across Icecrown Citadel to exact their vengeance on the Lich King, Arthas Menethil, before killing him and falling under the Frozen Throne's influence, becoming the new Lich King and enacting their new plans. In the set, they all appear as legendary hero cards.
- Malfurion the Pestilent: The death knight version of Malfurion Stormrage. He has been disillusioned with the druidic philosophy of the balance between life and death and sees that death always wins, so he cultivates swarms of insects to spread pestilence in order to reform the balance in his own image. He is a Choose One-oriented hero; when played he can either summon two Poisonous spiders of two Taunt scarabs, and his Hero Power lets him either gain attack or armor.
- Deathstalker Rexxar: The death knight version of Rexxar. After being corrupted, he released the souls that the original Lich King trapped, so that he could hunt them for sport. When he is played, he shoots arrows at all enemy minions, and his Hero Power creates a "Zombeast" made from two Beast minions stitched together.
- Frost Lich Jaina: The death knight version of Jaina Proudmoore. She first appears in the prologue when the Lich King defeats Jaina with overpowered cards, before raising her as Frost Lich Jaina to fight Tirion Fordring and his army of inexperienced adventurers. After defeating the Lich King, she takes the throne for herself and entices several undead to join her, but she doesn't notice her blood freezing. When she is played, she summons a Water Elemental and her Elemental minions have Lifesteal for the rest of the game, and her Hero Power deals damage and summons another Water Elemental if it kills a minion.
- Uther of the Ebon Blade: The death knight version of Uther the Lightbringer. He believes that the Light's justice has failed, so he will take justice against the wicked into his own hands. He equips his signature hammer, Grave Vengeance (which has Lifesteal) when played, and his Hero Power summons one of the Four Horsemen of the Ebon Blade. When all four are on the field at once, they all destroy the enemy hero and Uther wins.
- Shadowreaper Anduin: The death knight version of Anduin Wrynn. He believes himself to have been naive to follow the Light, and fully embraces the power of shadows, though in his entry quote he claims that the Light had betrayed him. He destroys all minions with 5 or more attack when played and his Hero Power deals 2 damage, and refreshes whenever he plays a card.
- Valeera the Hollow: The death knight version of Valeera Sanguinar. She has enhanced stealth abilities by disappearing into the shadows, which she uses to indiscriminately hunt people from the darkness. She gains temporary Stealth when played and her Hero Power creates a temporary "Shadow Reflection" card every turn that changes into the previous card that she played.
- Thrall, Deathseer: The death knight version of Thrall. He silences all of the trapped spirits once being corrupted, and feels lost without his link to the elements. He evolves all of his minions when played, and does the same with his Hero Power.
- Bloodreaver Gul'dan: The death knight version of Gul'dan. Gaining vampiric abilities after his corruption, the already power-hungry Gul'dan opened the Dark Portal and terrorized various worlds beyond. He resurrects his dead Demons when played and his Hero Power deals damage with Lifesteal.
- Scourgelord Garrosh: The death knight version of Garrosh Hellscream. After razing Azeroth with his power, he raised several undead followers and became an even bigger ruler than before. He equips Shadowmourne, which deals damage to adjacent minions, when played, and his Hero Power deals 1 damage to all minions.