vecna was born as a human, centuries ago as a member of the untouchable caste in the Flan city of Fleeth. He was initially trained by his mother, Mazzel, in the art of magic, before she was executed by the government of Fleeth for practicing witchcraft. Vowing revenge, Vecna eventually assumed a mastery of the dark arts achieved by no mortal before or since. He became a lich, Legend has it that Vecna was nearly slain in this battle by clerics channeling the power of Pholtus, the god of light. The clerics unleashed a great burst of light, which hit Vecna primarily on his left side. Vecna was rescued and brought to safety by one of his wizard generals, a cambion named Acererak.
Vecna eventually recovered. On the verge of conquering Fleeth, the officials of the city came before him to beg for mercy. They offered up the entire city and her wealth if only Vecna would spare the lives of her citizens. When Vecna was not satisfied, the officials offered their own lives. Vecna gave one of their number, Artau, and his family, over to his lieutenant, Kas, who spent the entire day torturing and murdering them before the other officials. Still unsatisfied, Vecna slaughtered all within the city, and had their heads stacked before the officials, with those of their family members prominent. Vecna then granted his mercy, granting the officials leave to depart, and promising them his protection for the rest of their lives.
At his empire’s height, Vecna was betrayed and destroyed by his most trusted lieutenant, a vampire called Kas the Bloody-Handed, using a magical sword that Vecna himself had crafted for him, now known as the Sword of Kas. Only his left hand and his eye survived the battle, perhaps because of the previous events in Fleeth.
Vecna did not stay gone forever, and rose as a demigod of magic and secrets, his cult helped set events in motion that would have granted him the power of a greater god, but the plan was ultimately foiled. After these events, Vecna ended up imprisoned in the demiplane of Ravenloft, but broke free again later, emerging with the power of a greater god, after absorbing the power of Iuz. He then broke free into the city of Sigil, where he came perilously close to rearranging all existence to his whims.