Izual is one of the villains from the computer game Diablo. He is the catalyst of all the events in the game, as he later turned out reveal the Heaven's secret that gave Diablo and his two brothers' advantage over their exile by the Lesser Evils' betrayal.
Izual was a lieutenant of the Archangel Tyrael, known as the greatest hero of The Great Conflict. Carrying the holy blade Azurewrath, he won countless battles for the heavens. After he learned that the forces of hell were forging the dark blade Shadowfang, he took upon himself the duty of destroying the cursed blade. Against Tyrael's advice, he led an assault against the Hellforge, which ended with his troops being completely annihilated and his capture. What Tyrael didn't knew was that this is Izual's personal plan all along.
Fed up with the Great Conflict, Izual, albeit reluctantly, sided with the powers of Hell and shared with The Great Evils his knowledge during his capture. He told the Prime Evils, Mephisto, Baal and Diablo the secret of the Soulstones: If their souls were imprisoned in a Soulstone, they could possess a mortal and use him to channel their full powers into the mortal realm, thus being able to reach the Worldstone, the source of the Soulstones and the artifact that held the balance over the world of Sanctuary. If they could corrupt the Worldstone, then they would ultimately prevail against Heaven. Thanks to Tyrael's foolishness to trust Izual, everything goes as planned and the three Prime Evils are able to manifest themselves into the mortal realm not long after they overthrowned voluntarily during Dark Exile. However, Izual had to pay a high price to do so; He had to sacrifice his angelhood by having his essence sealed with a demon's body, effectively making him became a demon for all of eternity.
As an adventurer follow Diablo and his brothers, he enters the Burning Hells aided by Tyrael, in order to find and kill Diablo. Tyrael asks the hero to kill Izual and save his soul from the forces of hell. The hero finds Izual in the Plains of Despair and slays his demon prison. The soul of Izual tells him that they were playing for fools all along, since everything was his plan despite the high price that he had to pay.
He later appeared among Diablo's army at climax of Diablo 3. However, he was struck down once more, this time by the nephalem hero.