The Burning Legion, also called the Great Burning Shadow, the Legion of the Lower Planes, or just the Legion, is an innumerable army of demons, infernals, and corrupted races that seek to destroy all order in the universe.
The creators of orders in the universe, the Titans, had become aware of the threat to all they had created posed by the dark beings existing in the Twisted Nether. These demons sought to devour all life energies of the universe and they eventually began to find their way into the Titan's world from the Twisted Nether.
In an effort to defend themselves, the Titans sent their greatest warrior, Sargeras, to serve as their first line of defense. A noble bronze giant, he sought and destroyed demons for countless eons, but during this time, he came across two demonic races. Both of them were intent on having universal power and dominance. Though Sargeras had nearly limitless powers which allowed him to easily defeat the demons, their corruption and all consuming evil troubled him. He began falling into a brooding depression due to his incapability of understanding the dark beings' depravity. As Sargeras fell deeper into his confusion and misery, he encountered another group intent on disrupting what the Titans had created, the Nathrezim (better known as dreadlords). This dark race of vampiric demons had succeeded in conquering a number of planets through possession of their people and turning them to darkness. The scheming dreadlords had turned whole nations against each other through manipulation and sowing mistrust and hatred. Despite Sargeras easily defeating the Nathrezim, their corruption still had a deep effect on him. After being exposed to the depravity of demons for so long, Sargeras lost faith in his mission and in the Titans' vision of order. He believed that the very concept of order itself was foolish and that the only absolutes in the universe were chaos and depravity. His fellow Titans tried to persuade him otherwise and calm his chaotic emotions, but Sargeras dismissed these optimistic beliefs. He left their ranks forever and set out to find his place in the universe, but though the Titans were saddened by his departure, none of them knew to what lengths Sargeras would go. As his form was mutated and his valiant spirit was consumed by his new madness, he decided that the Titans themselves were responsible for the failure of their creations. Sargeras decided to undo their work throughout the universe and to form an army that would ravage everything in existence. He shattered the prisons of the Nathrezim and the other demons he had imprisoned during his time in service to the Titans. Now free, the loathsome demons swore their loyalty to Sargeras, giving birth to the dark Titan's army, the Burning Legion. After coming across planet Argus, he found new beings for his army, the Eredar, highly intelligent beings that had a natural skill in magic. Amongst their ranks, Sargeras found two commanders for his army of destruction. Kil'jaeden the Deceiver, who would seek out the darkest of races to join the Burning Legion and Archimonde the Defiler, who would lead his forces into battle. Kil'jaeden's first recruits were the dreadlords, who served as his agents throughout the universe. They enjoyed locating primitive races for their master to corrupt and bring into the Burning Legion. A prominent dreadlord was Tichondrius the Darkener, who served Kil'jaeden as the ultimate soldier and sought to spread Sargeras' will throughout the universe. Archimonde had powerful agents of his own, the pit lords and their leader, Mannoroth the Destructor. From them, he hoped to create an elite fighting force to scour all life from the universe. Upon seeing his forces were amassed, Sargeras launched his forces into the vastness of the Great Dark and came to refer to this new army as the Burning Legion. Even to this day, it is unclear how many worlds they have consumed.
War of the Ancients
Over ten thousand years in the past, the Burning Legion was attracted to Azeroth due to reckless magic usage there. The Highborne night elves under command of the Queen Azshara and her counselor, Xavius, had been experimenting to draw greater amounts of energy to the Well of Eternity, Azeroth’s source of magical power. The Highborne’s reckless magic usage sent energy ripples spiraling into the Great Dark Beyond where it was felt by Sargeras. They drew him to their place of origin, leading to his discovery of Azeroth and his sensing of the limitless powers of the Well of Eternity. The dark Titan became consumed by an insatiable hunger and decided to destroy the young realm so as to claim its energies as his own. After gathering his great Burning Legion, Sargeras moved towards Azeroth with his demons ready for conquest and Archimonde and Mannoroth readied their forces. Queen Azshara was overwhelmed by the ecstasy of her magic and fell victim to Sargeras’ power, granting him entrance to her world. Her Highborne gave themselves over to the corruption and came to worship Sargeras as a god. To show that they were truly loyal to the Burning Legion, they opened an enormous portal within the Well of Eternity. With everything he needed in place, Sargeras unleashed his Legion upon Azeroth. The demons stormed through the well and swarmed over Kalimdor, leaving death, ash, and misery in their wake. Infernals rained from the sky, Doomguard marched across the land, and Felhounds ravaged the countryside. The brave Kaldorei tried to stand against the Burning Legion’s forces, but they were forced back inch by inch by the demon hordes. Malfurion Stormrage was the night elves' only hope and, after convincing his brother, Illidan Stormrage to give up his obsession with magic, set out to find Cenarius so as to muster a resistance. Conflict sprung up between the two brothers through Tyrande, who accompanied the two in the name of Elune. Malfurion and Illidan both had feelings for her, but it was clear that she preferred the druid. Illidan began to resent his brother’s romance with Tyrande, but his heartache couldn’t compare to his magic addiction. He had grown dependent on the empowering energies of magic and began struggling to keep control over his hunger to tap into the Well of Eternity’s power. With Tyrande’s support, Illidan restrained himself and helped Malfurion find Cenarius, who aided them in building an army, including the forest spirits and ancient dragons to fight the Burning Legion. The night elf forces rallied at Azshara’s temple and an all out battle with the demons erupted. As the conflict continued, Aszhara sat delusional, waiting for Sargeras’ emergence in Azeroth. As he drew closer to passing through the Well of Eternity, the night elf queen gathered her most powerful Highborne followers, since only a spell created by linking their magic together would be able to create a gateway large enough for Sargeras. Malfurion realized that the Well of Eternity was the demons' link to Azeroth and insisted to his colleagues that it should be destroyed. Despite their horror at the idea since it was the night elves source of immortality and powers, Tyrande realized that it was a wise idea. She rallied Cenarius and their comrades to storm Azshara’s palace and find a way to shut down the Well for good. Realizing that getting rid of the well would prevent him from using magic again, Illidan turned on Malfurion and the others to join the Highborne. He felt no remorse due to his addiction and resentment towards his brother for taking Tyrande from him and swore to defend the Well’s power by any means. Though saddened by Illidan’s leave, Malfurion lead a charge on Azshara’s throne room where the Highborne were unleashing their final dark spell to summon Sargeras. Thanks to Illidan telling her of the attack, Azshara was more than prepared for Malfurion’s force. The druid faced a massacre with most of his followers falling from the queen's powers. Tyrande attempted to attack Azshara from behind, only to be attacked by some of her guards. She managed to defeat them, but suffered grievous wounds and when Malfurion saw this, he swore to end Azshara’s life. As the battle both inside and outside the palace went on, the Highborne’s magic fell into chaos from the battle between the druid and the mad queen. The unstable vortex exploded, making the Well of Eternity collapse in on itself. Chaos erupted all throughout Kalimdor. The land split apart, the location of the Well was consumed by the sea, leaving an enormous Maelstrom, and the demons were banished back to the Twisting Nether. Azshara and her Highborne survived to be banished under the sea and become the vile naga.
Somewhere in Northrend, the Burning Legion invaded again and were fought by Aegwynn, who fought and defeated an avatar of Sargeras himself.
The Second Invasion
After their defeat at the hands of Malfurion, the Burning Legion watched and waited for a new attempt to invade Azeroth. Kil’jaeden was assigned to find a new way to invade and he was unwilling to take any chances on success. He decided a new force was needed to weaken the defenses of Azeroth before the Legion arrived. Kil’jaeden eventually discovered the world of Draenor, home of the orcs and the peaceful Draenei. He chose the orcs as his tools since they were bred as warriors and he bended the elder shaman, Ner’Zhul, to his will. The Legion later managed to gain complete control of the orcs after they were convinced to drink Mannoroth’s blood, cursing themselves to bloodlust and savagery. The orcs attempted to invade Azeroth two times through the Dark Portal, but were defeated by an alliance of the natives led by humans. After the Second War, the orc home world of Draenor was destroyed by Ner’Zhul’s attempts to escape to another dimension. With the orcs defeated and placed in internment camps by the humans, Kil’jaeden created a new force of harbingers by transforming Ner’Zhul into the Lich King, creating the Undead Scourge. Where the orcs had failed, the Scourge performed far better and managed to summon Archimonde to Azeroth and with him came the hordes of demon. After sweeping across the Eastern Kingdom, the Legion headed for Kalimdor to confront their old enemies, the night elves. Their main goal was the World Tree on Mount Hyjal, which contained the life essence of Azeroth and gave the night elves their immortality and powers. For the final battle, the humans, orcs, and night elves joined forces to hold back Archimonde and the Burning Legion’s forces while Malfurion cast a final druidic ritual on the World Tree itself. He gave the signal that all was ready and Archimonde was allowed to reach the tree. However as he began to feed on its power, the powers of the forest was unleashed and destroyed Archimonde in an enormous explosion, that also incinerated the surrounding forest.
AftermathWith Archimonde gone, Kil’jaeden became the Burning Legion’s leader and Azgalor returned to the Twisted Nether to plot for revenge. But their cultists are still scattered throughout Kalimdor and the corruption they sowed still remains in Felwood. It is primarily inhabited by satyrs and twisted furbolgs. The principal group of these remnants of the Legion is the Shadow Council, which is lead by surviving warlocks. Many demons also survived and still roam Kalimdor and they work with cults as a cohesive entity. The pit lord Magtheridon took over the realm of Outland, but was eventually overthrown by Illidan and his allies. A trio of dread lords, Balnazzar, Varimathras, and Detheroc were left behind to oversee Lordaeron when the Legion left for Kalimdor, but they were overthrown by Sylvanas Windrunner.
Attempts at a Third Invasion
Despite their defeat, the Burning Legion continues to invade planets. Kil’jaeden has sent his forces to Outland in an attempt to destroy Illidan for his failure to destroy the Lich King. However the fallen night elf’s forces have been able to match Kil’jaeden’s and they have so far failed to gain the advantage. During the invasion, the Burning Legion managed to open the Dark Portal and send their forces into Azeroth. But the forces of Azeroth managed to drive the demons back into Outland. Both soldiers of the Horde and the Alliance followed them into Outland where they have since battled the Legion’s forces. The Legion’s forces still engage in various activities throughout the realms and areas of Azeroth.