Astaroth is an antagonist in the Soul Calibur series. He is a creation of Fygul Cestemus, a pagan cult that worships Ares. Astaroth has appeared in every Soul Calibur game with the exception of Soul Blade.
Ares, the god of destruction, would not be pleased with the sword in this condition, he agreed to help the Azure Knight, Nightmare, build his power by collecting souls by slaughtering countless victims.
As Astaroth was finally ready to betray Nightmare and take the Soul Edge from him, Kilik, Xianghua, and Maxi stormed Ostrheinsburg Castle, and Astaroth was killed by Maxi. Four years later, signs of Soul Edge began to re-emerge, and Ares resurrected Astaroth in an attempt to retrieve the evil blade once again.
This time, though, his body had been infused with the shards of the Soul Edge, making him more powerful than ever before. Astaroth fought back against the curse, for he had become an ideal host for the Keres, because of the fragments of Soul Edge he had taken in during his resurrection.
He would destroy anyone who stood in his way, and now the cult had become nothing more than an obstacle in his path. Astaroth entered the temple to destroy the cult once and for all, and his whirlwind of destruction mowed down everything in his path.
The curse had become a crucible of chaos. He then proceeded to destroy the temple completely until it became unrecognizable debris, and nothing was left but chaos and rubble.
The cult's man-made giant, Astaroth, had always followed his masters' bidding, until one day 17 years ago, the creature developed a will of his own and rebelled; both Astaroth and Fygul Cestemus were destroyed.
But it wasn't long before the priests of Mars and Venus crafted a mechanical woman to retrieve Astaroth's core and return it to the cult, which had already begun to reform. Finally, his research bore fruit. Beaming with triumph, the high priest gazed upon the new Astaroth, as he roared and tore at his chains.