Nagash is the first necromancer, and one of the most powerful mages of all time. He caused the destruction of the civilisation of Nehekhara and created the Undead. He is himself a Liche able to command the undead.
The greatest in learning
Nagash was the son of King Khetep. He joined the Nehekharan Mortuary Cult and quickly became first and foremost among the priests of Khemri. Like all mortuary priests, he was searching for a means of achieving immortality. Despite his rank of High Priest in the Mortuary Cult, however, he coveted even greater power.
Though Nagash was already well versed in the magical embalming arts of Nehekara, it is said that a group of Dark Elf captives proved essential to his quest for immortality. One among their kind was a sorceress. She revealed everything she knew about magic to the High Priest of Khemri.
Nagash learned of the Chaos Gate in the far North and the Winds of Magic that blew from it, and how they may be harnessed by a careful practitioner. Unlike the sorceries of Khemri, which relied on the intercession of gods, Nagash learned that mortals could manipulate magic for themselves. He learned of Dark Magic and of how it coagulated into warpstone.
When the sorceress had outlived her usefulness, Nagash executed her companions, blinded the sorceress, removed her tongue and hands and buried her alive within his father's pyramid. With her knowledge, Nagash had become one of the few humans to truly master Dark Magic. He wandered the Necropolis of Khemri, summoning spirits of the departed and daemons with his new power, and learned great secrets.
King of Khemri
After the death of their father, Nagash's brother Thutep took to the throne, becoming the ruler of Khemri. But Nagash was now convinced to try a bid for absolute power.
One night, as the clouds covered the sky, Nagash slew his own brother, entombing him with their father. The next morning, his hands still covered with the blood of his brother, Nagash claimed the throne of Khemri for himself. As there was none other to gainsay him, the ascension was not contested.
Nagash used his new knowledge as the basis for a new branch of magic which he called Necromancy. This magic greatly extended his lifespan and enabled him to reanimate the bodies of the dead. Nagash ruled Khemri with fear, and forced countless slaves to labour for fifty years to build the greatest pyramid in Khemri from black stone, which would come to be known as the Black Pyramid of Nagash.
Nagash penned all of his knowledge and findings within several tomes made of human flesh and flourished with human blood. These works became known as the Nine Books of Nagash. Many others in Khemri flocked to his promise of immortality and power. The most notable among these was Arkhan the Black, Nagash's chief lieutenant, as well as a third of the Priests of Khemri.
However, the other Kings of Nehekhara were aghast at the reign of terror which Nagash had begun. Enraged at the corruption he had brought and the culture of fear and terror, the kings from seven other, lesser cities allied themselves in order to remove Nagash from his throne. A powerful army was raised to march on the legions of Khemri.
But Nagash was not to be so easily defeated. Using his Necromancy, he raised an army of the undead, a horde of skeletons to destroy the attacking armies. Such a thing was unheard of, and in the death obsessed culture of Nehekhara, it was recognized as the greatest of obscenities. Hundreds fled, terrified by the thoughts of battle versus the departed, however all was not lost. Although many did flee the sight of the dead army, the forces of the other kings rallied and Nagash was ultimately defeated, but not slain.
As Arkhan, the greatest swordsman of his time, gave his life to protect his master, Nagash fled to the north-east to plot his revenge against the lands of his birth in the Cursed Pit of Nagashizaar. It was generally decided at that time that all that Nagash had wrought during his accursed reign should be destroyed: the cabal of twisted followers he had ensnared to his ghastly practices were put to the sword, and great fires consumed much of what Nagash had done and written--his precious Nine tomes were believed to be among the ashes, though a very few copies managed to escape the wreckage. That all of his tomes were not destroyed would eventually come back to haunt Khemri and Nehekhara, just as the shadow of the Black Pyramid haunted it constantly.
The Great Necromancer
During this time, wandering in the desert, it is thought that Nagash came to the very point of death - only to cheat it and emerge as a Liche, the greatest of his kind, so much different of the ancient Liche Priests of the Mortuary Cult. He came to Cripple Peak and discovered there a secret deposit of warpstone.
Within the mountain he built his abode, a fortress-city to inspire terror and awe the world over - Nagashizzar. The mountain's highest peak was it's tower. Nagash learned how to manipulate the warpstone, and at Nagashizzar he forged many of his famed artifacts of power including his wretched sword Mortis, his Crown of Sorcery, and his Black Armour. Prolonged exposure to the mutagenic warpstone twisted Nagash into a hideous monster, no longer recognisably human. It increased his size and his strength but left him little more than a walking skeleton.
Such a large amount of warpstone drew other creatures, namely Skaven, who fought a massive war against Nagash for control of Cripple Peak. The Skaven armies were vast, but Nagash's magic abilities were also massive, as were his armies of undead. Nagash forged a truce with the Skaven though: he would give them warpstone if they would lure several Orc tribes into the pits beneath his fortress. The Skaven agreed, wary of his plans.
For hundreds of years the kings continued to rule Nehekhara much as they had before. In Lahmia the reigning Queen Neferata came across a copy of one of the Books of Nagash. She was captivated by the dark lore contained within and begun studying Necromancy.
Finally driven by her quest for immortality to make a pact with Nagash, she took an elixir distilled from his own blood. The moment the elixir reached her lips, Neferata's fate was sealed. She had chosen damnation and exile: Her heart stopped beating, and she became something both more and less than human. She became the first true vampire. Nefereta gathered to her the eleven greatest minds and champions of Lahmia, and gave to them each a portion of this elixir. They were the Master Vampires, from whom all other vampires in the world are descended.
Fearful of the wrath of the Gods, the famed King Alcadizaar of Khemri gathered together all the armies of Nehekhara and waged war on the twisted queen. Despite the powerful magics and armies of Undead unleashed by the vampires, the threat of Lahmia was crushed by a huge army mustered by King Alcadizaar. The queen fled Lahmia with a retinue of the six remaining Master Vampires she had created.
Those who fled were met by Nagash in the mountains of the north, and he embraced them as spawns of his own corrupt magic. These vampires became his captains. Nagash sent these undying warriors to make war with Nehekhara at the head of a mighty army of skeletons.
But Nagash had underestimated his former countrymen. Alcadizaar the Conqueror was the greatest general of his age (the 6th dynasty of Nehekhara) -- and some argue the greatest King to ever rule Khemri -- and led a unified army against the undead invaders. After many years of bloody war the hordes of Nagash were pushed back. As such the Vampire Masters decided to flee, with only W'soran remaining at Nagash's side eager for more necromantic lore. Nagash was furious and cursed all vampire kind to burn in the rays of the sun.
So bitter and evil was Nagash that he decided that if he was not allowed to rule all of Nehekhara then no-one could. He concluded that it was better to slay everything in Nehekhara than see it ruled by someone else. The first part of his plan was to get his Skaven allies to pollute the river Vitae, whose life-giving water the people depended upon. After he had tainted the river it became black and foul, and has since been renamed the River Mortis. Soon after the corruption of the Vitae pestilence ravaged the lands of Nehekhara.
Alcadizaar was forced to watch as first those he loved died, including his wife and children and then watched his beloved kingdom crumble before him. When a new army of the undead invaded Nehekhara, it was led by W'soran and Arkhan, whom Nagash resurrected as a powerful Liche. The meek defences put up to stop the invasion were easily thwarted and Alcadizaar himself was captured by the fell beasts. He was not executed though: instead he was thrown into a cell in Nagashizzar to be tortured at Nagash's pleasure.
It was now, with Alcadizaar imprisoned and Nehekhara on its knees, that Nagash revealed the conclusion of his evil plans. He began to weave one of the most powerful spells ever to be attempted. At the pinnacle of his power Nagash unleashed a mighty wave of sorcerous energy which washed over the land for hundreds of miles, causing everything that was living to decay and die, and all that was dead to rise again. Nagash planned to use his necromantic powers to raise the entire population of Nehekhara as an unstoppable army, which he would use to conquer the entire world, and there is little doubt he would have succeded, had a strange turn of events not taken place.
The Skaven leaders, the Council of Thirteen, watching from afar, realised the threat posed by this latest development. Still eager for control of Nagash's large deposit of warpstone at Cripple Peak, and aware that they would be amongst the first to suffer Nagash's wrath, the Council made the unanimous decision to assassinate Nagash. Rather than risk their own lives in an attempt to slay him, they decided to free Alcadizaar and provide him with the means to ensure Nagash's destruction. A powerful blade was made out of pure warpstone, a blade so deadly and volatile that even the wielder would eventually succumb to the effects--the Fellblade. Infiltrating Nagashizzar, a group of hooded Skaven agents freed Alcadizaar from his captivity and gave him the blade, departing without a word or a backward glance.
Still weak from the power he had exerted casting his immensely powerful spell, Nagash was recovering when Alcadizaar stumbled into his throne room. Surprising Nagash in his moment of weakness, Alcadizaar cut off one of Nagash's hands. Stumbling back, Nagash unleashed deadly magics at Alcadizaar. As he did so, his hand ran off into the shadows like a huge spider. Despite both being fatigued and weakened by their ordeals, the ensuing battle was titanic.
The Council of Thirteen, watching the battle unfold, joined their magic powers together to protect Alcadizaar from Nagash's onslaught, even as they were slowly being killed by Nagash's power. The battle lasted for an eternity, for even in his weakened state, Nagash was a foe to be reckoned with. But finally it was Alcadizaar who emerged victorious. Flying into a rage, Alcadizaar flew at Nagash and hacked away at him until he was dead and his corpse left in many small pieces.
Looking out across the land at his destroyed people, Alcadizaar fell into despair. He took Nagash's crown and stumbled around his empty kingdom being driven mad by his ordeal and the warpstone blade of the Skaven. Eventually he died, and the artefacts were taken up by others: the Skaven recovered the Fellblade, while the crown fell into the hands of the human shaman Kadon. The Skaven gathered every piece of Nagash's body and burnt them in fires of warpstone, scattering his ashes across the world. However they missed his hand--the dreaded Claw of Nagash.
One of the effects of Nagash's spell that the old, long dead kings of Nehekhara were brought back to life. However without the Great Necromancer's will to command them, they retained their free will, and were tended to by the Priests who it seems had finally reached their prophesied immortality. Thus, ironically through Nagash's attempt to destroy the lands of Nehekhara, he had given them a cruel mockery of life, creating the realms of the Tomb Kings.
Nagash did not stay dead. Using the power of his Black Pyramid, he was able to knit his body back together, piece by tiny piece, over 1,111 years. The next time he rose, he found the lands of Nehekhara defended by many jealous undead kings with their combined armies of skeletons equal to anything he could muster. Nagash challenged the reigning king of Khemri, the first King Settra, for the rule of Nehekhara. Settra and the other Kings, furious at what Nagash had done, chased him from Nehekhara. They had no fear of his monstrous form or the undead hordes he commanded, for they commanded skeletal legions of their own and had become just as monstrous in appearance as him.
Returning to his fortress, Nagash found the Skaven had mined most of the warpstone away. Nevertheless, in one night, he drove all the Skaven from Cripple Peak. The Skaven made many attempts at regaining Cripple Peak, but having been defeated by Arkhan who once again joined his master, they decided that they had gathered enough of the warpstone, and left Cripple Peak for good.
Nagash, still weak from his death, realised that he needed his old magical artefacts to reassert his power, including his stolen crown. So Nagash forged a new hand to replace his missing one out of a warpstone alloy. The crown had been taken north into the Badlands, where it fell into the hands of Orcs who raided across the Black Mountains and seemingly disappeared. Nagash led a great army into the nascent Empire to reclaim it but was defeated and slain by Sigmar at the Battle of the River Reik, having his skull smashed by Sigmar's mighty hammer Ghal-Maraz.
According to Mannfred von Carstein, Nagash's defeat at the hands of Sigmar resulted in a curse laid upon all vampires: for their refusal to come to his aid, they would forever be weak against the power of Sigmar. It has long been claimed that sufficient faith in any deity would be of aid against vampires, but it appears that the Sigmarite faith has additional potency against the undead.
In 2515 (two and a half millennia after the formation of the Empire) The powerful Orc Warlord Azhag the Slaughterer was killed in combat with Seneschal Kessler of the Knights Panther. His crown, which gave him sorcerous powers as well as nightmarish visions and insights uncommon for a Orc, was taken to the city of Altdorf and sealed in the Imperial vaults, where it remains to the present day. This is in fact the crown of Nagash.
Nagash once again returned to life, 1,666 years after his death at the hands of Sigmar, in the night known as the Night of the Restless Dead. It is thought he is again re-building his power. Though only a fraction of his former self, he is still one of the most powerful beings in existence, worshipped by some as the god of Necromancy. He knows he cannot be reckless again, so he bides his time until he can once more take on the world.
Its believed that he is currently enacting his will in the world through the manipulation of others, in particular Lichmaster Heinrich Kemmler and his henchman Krell, and even Mannfred Von Carstein, who had a talisman from Khemri origin that Nagash previously used to have complete control over the undead.