Those that did not live during the reign of The Necromancer find it difficult, if not impossible, to comprehend that such an entity existed. For those that witnessed that final event wherein The Emperor destroyed The Necromancer, one could scarcely believe the sight before them. All assumed that The Necromancer would be like in the tales of such death-workers from the Old World: decayed, decrepit, dead and yet not so. Nothing of the sort was true.
Instead, what we learned was that The Necromancer was once a horribly abused and neglected boy. When the Azure Flames erupted, he lay dying in a hospital on a table in an operating theater. He lay there because his mother beat him near to death out of a petty anger when the boy interrupted one of his mother's frequent unlawful couplings with a man. He knew not his father, and had no such figure around; he was unwanted, and his mother could not be rid of him, so she beat and berated him because she could not ever accept her own failure and responsibility.
It did not help that he came from a ghetto wherein a long-abused race of men, formerly slaves, got herded into generations before. The Old World rulers were not enlightened men, and in their decadence encouraged new forms of old ills; the result was poverty, ignorance and exploitation such that slavery for this race never truly ended- so neither did the reactions to it.
So, as the Azure Flames raced across the world, those charged with saving his life fled instead thinking him disposable and not worth the effort. Abandoned by the last people trusted to make right the wrongs in his life, the boy impotently raged and cried out for justice- for revenge. Unexpectedly, someone answered.
This someone called itself "Gabriel", and took on the appearance of a then-famous actor in a well-known role of the same name. Gabriel tells the boy that the Creator heard his cries, and sent him to offer the boy--now between life and death--the opportunity to be the instrument of judgement upon Mankind. The boy accepted without hesitation; all he had to give in return was his name, and what is a name to one like him? Of course the boy accepted, for the price was nothing to him; this is why no power known to Man can reveal The Necromancer's name- he gave it to someone beyond mortal ken in return for power beyond mortal ken.
This, reader, is how the great and terrible scourge of Man known as "The Necromancer" came to be.
As he desired revenge, he also desired all deprived of him before. He grew from a boy into a great and powerful man, tall and broad-shouldered, flesh hardened into a lean and powerful athletic form. His presence grew with his maturity, and the fear-filled form of a small, shattered son transformed into a muscular, magnificent man of power and authority. No decrepit form had he. No decayed corpse-flesh. No, his lungs breathed deep and powerful. No, his heart beat hard and fast to pump red blood through living veins. The Necromancer, in truth, was a magnetic man of power and none who saw him ever forgot it.
Gabriel was not his only adviser. As The Necromancer grew, he learned that he held absolute power over life and death, for he held power over the flesh and dominated the wills of the dead- all that ever lived were his to command, be they imprisoned in their dead flesh or not, and all flesh that he knew was his to command. This would, in time, become his undoing, but until those centuries passed as the remnant races of Men surviving the Azure Flames died out The Necromancer knew no fear. The greatest generals of history lead his legions of lifeless drones. The greatest admirals of history led his ghost fleets. The greatest politicians of history administered those living colonies permitted to persist. The greatest monsters of history terrorized one and all to ensure The Necromancer's reign would continue as desired.
This, reader, is one of the reasons for why The Necromancer was such a feared player in the Wars of the Damned that followed the Azure Flames and the destruction of the Old World. Imagine now what it took for The Archmage to hold him off until the White Tower People could stand on their own. Imagine now what it took for The Emperor to cast him down and destroy him forever. Imagine what it took for The Engineer to get past The Necromancer's defenses and join forces with those others to ensure that The Necromancer would fall.
Imagine, and be glad that you live now long past that terrible era.