Killzone is a first-person shooter exclusive to the PlayStation 2. A sequel, Killzone: Liberation was released on the PlayStation Portable and another followup, Killzone 2 was released for the PlayStation 3 on February 27, 2009. Killzone 3, the fourth installment in the series, was released February 22, 2011.
The game is set in an era of space colonization where the Helghast Empire has recovered from its defeat in the First Extrasolar War and launched a blitzkrieg against the outer Interplanetary Strategic Alliance (I.S.A.) colony planet Vekta. Vekta's orbital Strategic Defense (S.D.) platforms failed during the initial assault, allowing the Helghast to land swarms of soldiers onto the surface and making it all the more difficult for the outnumbered I.S.A. forces.
In the game, the Helghast are a faction of human descendants who colonized the planet Helghan many generations ago. The planet's harsh environment forced the Helghast to adapt and mutate so much that they can no longer be considered human. They are stronger, faster and more resilient than their human cousins, and possess a burning hatred for humanity. Except for a small number of half-breed Helghast and trained troopers, they require a gas mask and air processing tank that creates air similar to that found on the planet Helghan. Earth, after a serious nuclear war between its nations, formed a major government of the richest surviving government and industries to explore space colonization, eventually settling for solar system outside of Sol. They find the Alpha Centuri which contains two planets next to stars, one lush and blossoming Vekta, another rich in energy supply but inhospitable; Helghan. These two planets were invested by the Helghan Corporation after the UCN (United Colonial Nations) decided to auction it. However after Helghast's different economic policy threatened to undermine the UCN's financial system, the UCN invaded Vekta and removed the Helghast after failing to impose financial sanctions. This left the Helghast deeply resenting the loss of Vekta and the forced colonization of Helghan, a harsh and brutal planet.
The player takes control of I.S.A. Captain Jan Templar, who is desperately repelling the invasion in brutal trench warfare and epic house-to-house clashes, but despite the ISA's efforts they continue to suffer losses and Helghast slowly prevail, their relentless advances coercing the ISA soldiers backwards against the surging Helghast forces. Templar and his squad are called back to the base for reassignment. However, the ISA HQ is overrun by the overwhelming assault force of the swarming Helghast and a forced evacuation is conducted. Believing that he has successfully negotiated his way past a heavily-armed Helghast, Templar advances; however, the Helghast is actually targeting Templar, until an ISA assassin stealthily stabs the Helghast. The assassin is Shadow Marshal Lugar, Templar's ex-lover. Templar and Lugar are promptly sent to find the I.S.A. operative Gregor Hakha and the vital supply of information he holds. Before finding Hakha, Templar and Lugar confronted a daunting prospect as several Helghast tanks and soldiers closed in on their position, unaware of the ISA soldiers who are ultimately rescued by an ISA soldier called Sergeant Rico Velasquez who harbours deep loathing towards the Helghast for the brutal slaughter of his original unit. Rico willingly agrees to join Templar and Lugar- after they rescued the held-hostage Vaughan- sensing Helghast blood. As their exhausting venture continues, they eventually track Hakha, but to their disbelief he is a half-Helghast spy. Unsure whether to trust him, they press on through the docks where a series of devastating conflicts occur as ISA ambush heavily-guarded Helghast positions and regain the docks -after a rousing rally cry from Templar to defuse the tension in the unit- a strategic place in Vekta, as the epic and vicious duel at the docks progresses the unit discovers that General Stuart Adams, a high ranking ISA officer, is a traitor and a servant of Joseph Lente (the commanding General of The Third Helghast Special Forces Army) and was responsible for sabotaging the SD platforms, rendering them unable to defend against the Helghast. The Earth Defense Fleet (EDF) go to assist the Vektan Army, however Adams kills General Vaughan and receives his security key, allowing him to reboot the platforms, and prepare an ambush for the EDF relief force. Templar's mind becomes fully focused on killing Adams, for the death of his godfather Vaughan who raised and trained him after Templar's father -Dirk Templar, a friend of Vaughan- died as an ISA soldier. Slowly the ISA unit begin to penetrate the heavily-reinforced positions held by the Helghast, their ventures destabilizing the Helghast military and technologies, and proving a significant disruption for the Vektan invasion itself as the ISA unit targeted bridges, cyber-bot activation bases and guard towers. Lente, frustrated by Adam's endless failures to kill Templar's unit, seizes control of the invasion force and calls on powerful bodyguards and soldiers to secure defensive positions, but fares no better as the ISA unit again tear through the Helghast defences with outpouring fury.
Templar and the others confront Lente, only to find out that Hakha was a chief-of-staff for him. Lente says that Hakha's family was ashamed to even be related to him, except his brother, who talked of his heroism. Because of this, Lente had Hakha's brother shot down. With anger in his eyes, Hakha shoots Lente, killing him. From this moment it is can be suggested that Rico obtains increasing respect for Hakha accelerated by what he witnessed, while Templar and Lugar will no longer question his devotion to the ISA cause.
The battle progresses through snow and icy mountains as the ISA unit saunter through harsh climates, tracking possible traces of routes to the Orbital SD Pltforms to assassinate General Adams and the concealed and suspected romance glowing between Templar and Lugar occasionally is revealed fully as Hakha explains to Rico that Templar and Lugar were deeply in love at one point, however Templar's attempts to draw closer was maligned by Lugar's distancing accelerated by Lugar's inclusion into the Shadow Marshall Regiment, and the breaking of the relationship. Nine months later to present day, they are reunited in unfortunate and difficult circumstances.
The unit travels to the SD platform, heavily swamped with Helghast of all ranks. Assigned with separate tasks, the ISA soldiers successfully complete their objectives, mainly to engineer the destruction of the SD infrastructure and call off ISA attacks on the station. However the unit is captured while Breaking out, Templar and his fellow colleagues realize the SD platform is breaking apart and Templar suggests they hold secure their current point while he pursues Adams, eventually wounding him gravely in a brief exchange of gunfire. However, Adams survives the fight and escapes only to be crushed by falling debris as the SD platform explodes after its infrastructure fails.
While Rico and Hakha fall asleep after their exertions, Templar and Lugar discuss quietly the future for Vekta, a moment to rekindle their lost romance instead lost again to their duties to Vekta, prize colony of Earth.