The Undead are a fictional undead race in Blizzard Entertainments Warcraft video game and book series.

[edit] History
The Undead were originally used by the Necrolytes and Death Knights of the First and Second Wars, however that practice stopped after the death of Gul’dan and the abolishment of Necromancy by Thrall, the warchief of the New Horde.

The new generation of undead was created by the Lich King, Ner’zhul who had been transformed into a higher being by the demon lord Kil’jaeden. Once an Orcish shaman, Ner’zhul sought warlock powers and delved deeply into demonic magic, until he was confronted by Kil’jaeden, the dark lord of the Burning Legion. Ner’zhul bargained with the demons – in exchange for incredible power he would pledge the service of the enslaved Orcish horde to the demons, and open portals for the Horde to invade Azeroth. After his defeat by the Alliance his body was ripped to pieces and his spirit tortured, until Kil’jaeden decided to use him as the leader of a new invasion of Azeroth. As a check on his minion’s tremendous new powers, Ner’zhul, now the “Lich King”, was embedded in a great glacier in Northrend and watched over by vampiric dreadlords.

The Lich King was able to reanimate the body of any being that had fallen. After recruiting the Prince of Lordaeron, Arthas Menethil the second during the Reign of Chaos attacked Quel’Thalas, the High Elven kingdom. The Elves fought against the Scourge, but the Scourge were triumphant and assimilated Sylvanas Windrunner and most of the High Elves into the undead.

[edit] Undercity
The city of the Undead in the Warcraft Universe is the Undercity, resides underneath the Ruins of Lordaeron, built by Arthas Menethil before being forced back to Northrend to come to the aid of the Lich King.

It is interesting to note that the entire above-ground section of the Undercity is not protected by any NPC guards, though there are guards in front of all the entrances, and the inside of the city is very heavily guarded.