Omega (オメガ, Omega?) is a Weapon that appears in Dirge of Cerberus -Final Fantasy VII-. Unlike the other Weapons, who were created to protect the Planet from a great threat, Omega serves as a last resort; when all life on the Planet is threatened, Omega is born. Chaos, another being born with Omega, sends all life to the Lifestream. In the wake of this event, Omega takes the residing and incoming Lifestream into its being, and when finished, it flies into space. From there, the cycle of life begins anew.
The Planet, however, without the power of the Lifestream, becomes a barren rock devoid of all life. The Protomateria, which allows Omega and Chaos to be controlled, is a special Materia created by the Planet to prolong and delay its inevitable fate.
A group of elite soldiers called the Tsviets seeks to awaken Omega under the influence of Professor Hojo (who is masquerading as its leader, Weiss the Immaculate). By gathering those untainted by Jenova and slaughtering them, the Tsviets are able to trick the Planet into thinking its life is threatened.
When Vincent Valentine confronts Weiss in an attempt to prevent Omega's birth, he learns that the man is being controlled by Hojo, who uploaded his mind to the Worldwide Network prior to his death. After revealing himself to Vincent, Hojo describes the search for a host strong and pure enough to fuse with Omega that led him to Weiss, but his plan is ruined when Nero the Sable, Weiss's brother, taints the Tsviet leader's body with G-Substance.
Despite the efforts of Vincent and his allies, Omega is summoned. In the end, Vincent uses the power of Chaos to stop it. Both Chaos and Omega return to the Planet upon the Weapon's defeat.