Sigmar Heldenhammer is one of the pivotal figures in the "history" of the Warhammer world, also known as the Old World.

In the annals of recorded history, when the Dwarf Empire still crossed the undermountains and the Winds of Magic still blew strongly, Man was in its infancy as a race. They lived in small tribes, and to one such tribe, the Unberogen tribe, Sigmar was born. Sigmar grew strong and quick, and became leader of his tribe. He managed to bind many of the other splintered tribes to his own. He rescued the Dwarf King in a raid on an orc encampment, forever earning the gratitude of the Dwarf King. In return, the Dwarfs taught man the secrets of ironwork and gunpowder weapons. Alaric the Mad, a master Runesmith was commissioned to work twelve great swords for Sigmar and his tribe. Sigmar himself was given the mighty hammer Ghal Maraz, the skull splitter. From then on the invading orc armies met the combined forces of men and Dwarfs, and were consistently driven back. Sigmar did many other mighty deeds, including destroying the corpse of the great Necromancer, Nagash the Black.

Sigmar was crowned the first Emporer of the Empire, currently the largest collection of lands held by Humans. Sigmar ruled for roughly fifty years, and then journeyed east, never again to be seen. Within a generation, Sigmar was openly worshipped as a god.

Note: Most of this was paraphrased from Warhammer Armies: Empire, published by Games Workshop.