The Scourge was created by the Burning Legion as a tool to aid them in taking over the world of Azeroth, in order for the vast hordes of undead not to run rampant however they needed to create one being that would be completely dedicated to controlling the mindless horde telepathically, thus they sat their eyes on the orcish shaman Ner'zhul who they believed would make a perfect candidate due to both his strength and previous dealings with the Legion. Ner'zhul's mortal form was completely destroyed by the Legion and his spirit was trapped in a block of ice and put on the Frozen Throne in the Icecrown Citadel of Northrend, there he would sit in service of the Legion and in control of the Scourge, but now known as The Lich King.
When the invasion of Azeroth begun the Legion ordered the Scourge to attack the worlds inhabitants in order to spread chaos and weaken them before the Legion's arrival. It was during this time that the Lich King would momentarily be able to break free of the legion's grasp just enough to draw Arthas Menethil towards him, Ner'zhul and Arthas would eventually merge which gave the Lich King a physical form, and after the Legion's eventual defeat he would lead the Scourge in various campaigns against the other inhabitants of Azeroth.
When Arthas was eventually vanquished by the paladin Tirion Fordring with the help of other heroes, the disfigured warrior and former Regent of Stormwind Bolvar Fordragon takes his place as the new Lich King, becoming the Jailor of the Damned. For without a Lich King, the Scourge would run rampant across Azeroth.
The Scourge was created in 2002 by Blizzard Entertainment as a major faction for their hit RTS game Warcraft 3: Reign of Chaos.
The Scourge is primarily made up out of various types of undead creatures but also constructs and humans, especially Necromancers and Cultists, some of the main types of creatures found within the Scourge will be listed here.
Cultist Of The Damned - These cultists are devoted followers of The Lich King, they were instrumental in the invasion of Azeroth and are lead by The Lich King's right hand man, the Lich Kel'thuzad.
Necromancers - The Necromancers are dark spell casters that focus on Death Magic.
Skeletons - The Skeletons are some of the most basic units of the scourge, typically serving as front line fighters or cannon fodder.
Ghoul's - Ghoul's are another basic unit in the Scourge, typically used as front line fighters in big numbers or as workers.
Crypt Fiend's - Crypt Fiend's are huge undead spiders raised by the Lich King, there are several different sub-types of Crypt Fiends. One of the Lich King's strongest generals Anub'arak came from this category.
Gargoyles - Gargoyles are flying monstrosities with the ability to turn to stone in order to heal their wounds.
Abomination's - Abomination's are huge hulking creatures sewn together from different body parts, they typically fight with chains and hooks and can exude a vile stench from their rotting bodies harming nearby enemies.
Banshee's - The Banshee's are spectral ghost-like creatures that are typically very magically proficient.
Shade's - The Shade's are the willingly given souls of cultists, a typically shade has none or very limited combat abilities, instead they use their vaporous bodies and keen senses to spy and gather information.
Liches - The Liches are typically raised from very powerful spell casters and retains the ability to cast powerful spells even in death, Liches are some of the most powerful and valuable members of the Scourge.
Frost Wyrm's - The Frost Wyrm's are some of the largest and most powerful creatures in the Scourge, raised from dragons they take the shape of a massive bone dragon with a powerful frost breath at their disposal.