Faultline was a Superpowered being responsible for the leveling of Overbrook, and the resulting creation of the Faultline city zone.
The Official Story
According to the official story, right after the Rikti War, the Archvillain Faultline tried to blackmail the city with his earthquake devices. A few minor heroes, including Blue Steel and AkashiKnight tried to stop him, but failed, AkashiKnight himself dying in the process. The villain set off his machinery and leveled Overbrook. No one has heard from Faultline since, and the area adopted his name until this day.
The Issue 8 Faultline story arc however brings new light to the events that levelled Overbrook. Through completion of this arc it is revealed that Faultline was actually a Hero and a close ally of both Blue Steel and AkashiKnight. On the day Overbrook was destroyed, Faultline became the unfortunate victim of PsiCurse and his PsychoChronoMetron, a device used to convert psionic energy into temporal energy, allowing him to psychically rewrite the past. PsiCurse attempted to use the device to turn his arch-enemy Faultline into his ally, but the plan backfired when feedback from the device caused Faultline to lose control of his ability to create earthquakes, resulting in Overbrook's destruction. Both AkashiKnight and PsiCurse died in the resulting earthquake, whilst Blue Steel escaped, along with Faultline's young son Jim Temblor.
A New Faultline
These rumors are confirmed when players encounter Jim Temblor in Vanguard story arcs, having taken the name Faultline.