Vecna and his mother, Mazzel, were born to the untouchable caste in the Flan city of Fleeth. She trained him as a wizard in the arcane arts for many years before the city burned her as a witch, and Vecna escaped. He then studied under the direct tutelage of Mok'slyk, the Serpent, said to be the personification of magic itself, whom his mother had served as a priestess.
One thousand years later, Vecna had risen to become the most powerful wizard in the land and had already achieved lichdom having carved an empire for himself in the Sheldomar Valley. During this time, he wrote Ordinary Necromancy and made significant contributions to The Book of Vile Darkness. He marched on Fleeth with an army of undead and spell casters. He was nearly destroyed by clerics channeling the power of Pholtus, god of light, when they blasted him with a beam of light on his left side. He was saved by one of his generals, the half-fiend Acererak. Acererak would become a mighty lich himself.
Once recovered, Vecna attacked the city again. This time, the leaders of the city begged for mercy, offering wealth and eventually their lives in exchange for their citizens. Vecna turned one of them and the man's family over to his lieutenant, the vampire Kas The Bloody-Hand, who spend a day torturing and killing them, then had all within the city slaughtered and their heads mounted on pikes.
At the height of his empire Vecna was betrayed by Kas. Kas managed to destroy the Archlich before his own death, with the Sword of Kas, a lethal blade of the Undying Kin's own make, leaving only Vecna's left hand and left eye behind.
Vecna eventually returned and by 581, had risen to godhood. He absorbed Iuz, becoming a greater god and attacked Sigil, the City of Doors in an attempt to rewrite the universe in his own image. He was thwarted by a group of adventurers and ejected from the city, which freed Iuz, but allowed Vecna to stay a minor god and return to Oerth.