Dorghar is Archaon's Daemonic mount, his massive winged form swollen upon the souls of his vanquished foes. Such is the fell sorcery coursing through Dorghar's blood that the foes he consumes never truly die -- instead, their souls are trapped within his gut and their tormented faces mark his hide.
During Archaon's long war across the Realm of Chaos, each of the Dark Gods sent a daemonic champion to slay him. As Archaon crushed each challenger in turn, Dorghar drank the soul from its shattered carcass.
With each draught of malefic power he underwent horrific transformations, sprouting monstrous heads twisted into the likenesses of those he had slain. Only Slaanesh, in his mysterious absence, failed to send a champion.