Sigmar is one of the protagonists of Warhammer Fantasy
He is the once mortal man who united the human tribes to found what wound become the empire. He was latter worshipped as a god by the people of the empire after his dissaperence.
Sigmar was once a man born in the unbrogen tribes. After helping the dwarf king Kurgan Ironbeard, Sigmar recieved the legendary warhammer Ghal-Maraz, the Splitter of Skulls, and forged a lasting alliance between men and dwarfs. He latter founded the empire by uniting all the tribes of men. He ruled as emperor for a time before leaving his throne misteriously. Latter generations worshipped him as a god.
Many years latter, during the end times, Sigmar came back to his people and became the incarnate of heaven. During the final battle for the old world against Archaon, he fall into a vortex as the wolrd is destroyed.
While floating in the void, Sigmar met the star drake Dracothion who send him to the mortal realms. There Sigmar unite the gods and the mortal races into a great alliance and civilisation prospered. Then the forces of the dark gods came and shattered the armies of order after a long war that saw Sigmar lose his precious warhammer. Filed with sorrow and rage, he retreated to seclusion in the Realm of Azyr, sealing the gates behind him.
During the centuries of the age of chaos, Sigmar formed the sormcast eternals from the souls of the mortal heroes and made them into a powerfull army. After a long preperation, he unleashed his forces upon the forces of chaos in an bid to reclaim the mortal realms.