Omega was the most powerful Thanosi. He and the other Thanosi were freed and activated when the cosmic anchor known as Atlez attempted to set events in motion to aid him in securing his replacement. Near death and time dwindling, Atlez launched a meteor, in desperation, at one of Thanos' home bases, severely damaging a section of the base and freeing several Thanos clones.
Combining his genes and purloined DNA of Galactus through various means, Thanos created Omega. Though due to Omega's incredible power and a mental flaw that was exhibited in the Thanosi, Thanos never intended to activate him.
Omega was created by Jim Starlin and Al Milgrom and first appeared in Infinity Abyss issue 3 (2002).
Major Story Arcs
A new Entity
While the other clones worked together in a plot to end existence, Omega set out alone. However, he too shared the flaw that made the clones seek to usher in oblivion. He began to consume several planets to build up his power levels to aid in this goal.
Through very careful and strategic moves, Thanos and his allies were barley able to defeat Omega. Though ultimately successful, the attempt nearly cost Thanos and several of Earth's heroes their lives.
Powers & Abilities
Omega possessed all the same powers as Earth-616's Galactus and Thanos, but on a far greater scale. He also shared Galactus' insatiable hunger. Omega lacked the gift of speech. Also, being an incomplete project, he suffered from reaction retardation - his only true weakness.