DK, the abbreviation of DeathKnght, is a soldier in the Undead Scourge Corps. It was formed under the leadership of the Lich King to fight against human paladins. However, when this army was formed, there was no outstanding leader like Wu Se, the Messenger of Light. Therefore, the Lich King searched in many ways and chose Prince Arthas as the supreme leader of this army. Then, taking advantage of the invasion of Lordaeron by the dread Lord Melganis, the invincible magic sword Frostmourne (this sword was cast by the witch herself and invited by the king) can seize the enemy's soul, and those killed by this sword will become undead. Baron rivendell of STSM and Sylvanas Windrunner, a ranger in Silvermoon City, became the leaders of the undead after they were killed. As bait, Prince Arthas degenerated and eventually joined the Scourge, leading the Death Knight to continue to invade Lordaeron. (WAR3 version of Chaos tells this history. )

Later, Prince Arthas defeated Kilgardan, one of the leaders of the Burning Legion, went to Northrend, the hometown of the scourge of the undead, and destroyed Illidan, the frozen throne. He boarded the frozen throne, broke the ice coffin that imprisoned the lich king's soul, and released the lich king's soul (and the lich king died). And put on the crown of the Lich King and became the new supreme commander of the undead scourge (WAR3 Frozen Throne Edition tells this history).

As can be seen from the above, the DK in the WAR3 mission is Prince Arthas himself. Blizzard shows us how predestined a man is with his fall, and every minute has a different ending. DK in battle is another name.

The death knight in the DK area of WOW is not Prince Arthas himself, but his soldiers.

The real Prince Arthas himself is still in Northrend, and he is trying to build the fortress of the Ice Throne. Blizzard will open Northrend-related versions when the fun of Burning Expedition is exhausted in the future. At that time, everyone can face the real Prince Arthas himself in WOW.