Sigma was the prelate of a parallel earth at the edge of destruction because the over-explotation of their own resources and the pollution of its ecosphere. Depiste this, Sigma still was a ethical person and because of that he opposed to the plan of Damocles to steal the life power of parallel earths to feed their dying world. When Damocles tried to start his machine Sigma tried to stoped but he was absorbed in the machine, losing himself in the myriad of worlds.
Sigma reappered as a newborn baby in front of the analog of Damocles, Dr. Tsung in the main Wildstorm earth. Tsung adopted him and gave him the name of Ethan McCain. Unknowing to him, Ethan become the origin of the Gen-Factor, an element used to give superpowers to several individuals. This gen-factor was used specially by the agency IO and Miles Craven.
Fire from Heaven
When the members of Team 7 started to die because of the unstable gen-Factor was extracted from them, Kaizen Gamorra, allied with Miles Craven tried to reach the original source of the factor, Ethan himself. However at that moment Ethan started to manifest his own powers and defeated the Zombots send to capture him. However he was not a rival to the Sword of Damocles, who captured him and Tsung.
Once in Gamorra, a taste of Ethan dna was used to create the Gen-Omega, a clone hosting the mind of Miles Craven. However it was here where Damocles discovered Sigma alive, depiste he had no idea who Damocles was. However he rallied with the other heroes when his adoptive mother and sister where abducted by Damocles. With the help and sacrifice of Deathblow, Sigma pushed Damocles outside their reality.
When the members of Gen 13, Fairchild, Freefall and Grunge traveled to space, they found themselves in a dystopic future where his protector Lynch had become a tyrant worse than Miles Craven. In this future, a more mature and expert Sigma was part of the rebelious forces opposed to Lynch, leading the sons of Gen 13, called Gen 14.
He was one of the SPBs freed from TAO's cryogenic prisions prior to Armageddon.
Ethan draws his powers from many parallel dimensions through a nexus in his genetic structure. This allows him to mimic any Gen-Active power that could possibly exist. And he was the key to save the dying members of Team 7.