Prior to his defection, he was a trusted aide and friend to General Joseph Lente, the mastermind of the Helghast invasion of Vekta. At one point, Hakha even served as Chief of Staff to Lente. Hakha has a brother, and it is known that his mother is Helghast and his father Human. He is an expert in Helghast weaponry and technology, as possesses strong technical and espionage skills. He also heals faster than an ordinary human. He is wise and very intelligent, judging by his vocabulary, and sometimes quotes philosophers and poets alike.
Holding the rank of Colonel, Hakha defected to the ISA shortly before the invasion of Vekta, opposing the authoritarian nature of Scolar Visari.
Hakha was immediately marked for assassination by the Helghan invaders during the invasion. Shortly after his ISA bodyguard was struck down, he was rescued from certain death by Captain Jan Templar, Sergeant Rico Velasquez and Shadow Marshal Luger. Although Hakha was greeted with surprise and hostility (most especially from Rico) over his Helghan heritage, in which Rico attempted to execute him but prevented by Templar. Hakha proved his trustworthiness to his rescuers by saving Rico's life from a Helghast soldier.
Hakha joined Templar's squad and was set to be evacuate from Vekta. However, Hakha requested Templar to hack into the ISA mainframe to extract information on the SD platform, which he believes has fallen to the Helghast. He was then accused by Rico of being a double agent working for the Helghast and is only attempting to disrupt the ISA. This provoked a tense stand off with Rico and Luger (who believed in Hakha's claims) until it is defuse by Templar, who gives Hakha permission to analyze his findings. Hakha's suspicions proved to be true as ISA General Stuart Adams, commander of the SD platform, is working for Lente and intends on using the platform against the UCA relief fleet.
Hakha fought alongside Templar's squad in trying to stop General Adams. Throughout the entire journey, Hakha often clashes with Rico over his Helghan heritage but eventually the two come to respect each other. They eventually intercepted and defeated Lente. Hakha shared some words with mortally wounded Lente, criticizing him for being not the friend he once knew and having "sold his soul" to Scolar Visari for power. Lente in turn spites Hakha by revealing that his family saw him as a disgrace, except for his brother who accepted Hakha's "heroism" and was personally executed by Lente. Upon hearing this, Hakha promptly shot Lente dead.
Hakha and the others then used Lente's shuttle to reach a nearby uplink and traveled to the platform just as the relief fleet arrive. The group managed to stop Adams before escaping to a shuttle as the fleet bombard the platform. When their shuttle is unable to launch due to being connected to a fuel line, Hakha attempt to disconnect it but becomes trapped under it when being attack by Helghast forces. Fortunately, Rico pulls Hakha out to safety. Afterwards, Hakha thanks Rico for saving his life.
While he does not make an appearance in following games, it is believed that he retired his military commission and aided the Vektan Council in preparing for their counterattack against Helghan, even suggesting that Luger be dispatched to eliminate Scolar Visari and end his threat once and for all.
- "You try to compare us?... You made a choice, General, based on your own goals and morals. As did I. We may both seem traitors by our outside appearance, but that is where our common ground ends."
-his reply to General Adams when being compared to himself.
- "Given time, even a monkey could write Shakespeare." - in response to the squad's agreement with Rico's idea of a head-on attack against a Helghast code 3-3 firebase.
- "Well, those of us with even remotely developed minds rise above the frailities of the flesh, and cope with it." - in response to Rico's anti-Helghast attitudes following his rescue.
- "Right, well, a special forces captain falls in love. He promises her the world, but she has other plans. Nine months later, they meet again, except now the brave captain's sweetheart is a cold assassin. Trained to kill. Trained to think, not feel. Act, not reflect. Oh, she's almost perfect. Though I doubt Captain Templar feels otherwise." - explaining to Rico the nature of Templar and Luger's relationship.
- Gregor Hakha is voiced by Sean Pertwee, who also voices Colonel Mael Radec in Killzone 2. Sean Pertwee is the only voice actor in the series to play Helghast characters against and in support of Scolar Visari.
- The StA-52 assault rifle is Hakha's favoured weapon and shows above-average accuracy with it.
- Hakha is the first known "half-breed" in the series.
- He is the first playable Helghast in the campaign mode of the Killzone series. Echo of Killzone: Shadow Fall is the second, though only in one level.
- He can pilot an Overlord Dropship.