The Void Hunters are a special mercenary group created by the Council to combat the Peacebringer/Warshade threat currently growing in Paragon City. The Council have been hiring them out to other groups to help deal with their Kheldian enemies, as well as to make a slight profit. For those who don't want to deal with the Council's mercenaries, they sell Quantum Array Guns, thus creating the "Quantum Faction" to each villain group.
Void Hunters have received special training, Nictus fragment implants, and weapons that are particularly effective against Kheldians. The Nictus fragment implants give them high resistance to Kheldian energy blasts. Higher ranked Voids have been implanted with so many Nictus fragments that they can even absorb both energy and negative energy blasts. They are a threat to both Kheldians and non-Kheldians alike. However their weapons use a special quantum wavelength, designed specifically to disrupt the energies that make up a Kheldian. This forcibly rips Kheldians and their host apart. The damage can be healed over time, but too much of this can rip a Peacebringer or Warshade apart; killing them. This is a Void Hunter's goal.
Void Hunters will not spawn unless you are "flagged" for them. Kheldians are always flagged to have them spawn. Non-Kheldians who team with a Kheldian become flagged for them as well. A non-Kheldian who has been flagged to have Void Hunters spawn will continue to see them spawn until they log out, even if they are no longer teamed with a Kheldian.
Due to the second Rikti invasion, the Rikti are now hostile to all other enemy groups, including the Void Hunters. If a Void Hunter spawns within a group of Rikti, the Rikti will turn on the lone Void Hunter, and more often than not, the Void Hunter will fall before the Kheldian players approach the group.
Longbow and Vanguard will not tolerate Void Hunters within their presence either. If the player is in a place where they can fight either group (such as some Rikti War Zone missions) and a Void Hunter spawns within the group, they will be immediately attacked.
Quantum Array Guns, as seen below on the power lists, normally do Negative Energy damage to all classes, along with Slow. Against Kheldians (the Peacebringer and Warshade), it will do extra Negative Energy damage, as well as having a chance to Stun and Knockback.
Void Seekers are the lowest rank among the deadly Void Hunter mercenaries, serving mostly as scouts to detect possible Kheldian activity. They carry a powerful Quantum Array Gun specially designed to damage and disrupt Kheldian energy signatures, and have special Nictus fragment implants that protect them from energy attacks.
Void Stalkers are drawn from the ranks of Void Seekers who have proven their cunning and viciousness in battle. Extra training, more powerful Quantum Array weaponry, and additional Nictus fragment implants transform them into something dangerous to most heroes and deadly to Kheldians.
Void Slayers are the deadliest operatives the Void Hunter mercenaries have at their disposal. They carry the most powerful Quantum Array weapons available and have dozens of Nictus fragment implants, allowing them to destroy a Kheldian with little risk to themselves.
Prior to the February 12, 2008 patch, Void Hunters and Quantum Gunners would do bonus Nicti damage to Kheldians, which was unresistable. Currently, they do bonus Negative Energy damage.