Halo may get compared with many of its contemporaries, but there's always been one thing that separated Halo from its competition: the story. While many other shooters default to the tired "there's a war to fight" story, Halo has always been a part of a vast universe — sure, the stories aren't the most complex, but they're a cut above most other shooters on the market.
With Halo 5: Guardians just a few weeks away from hitting store shelves, it's time to go back and look at what made Halo what it is today. While some expanded universe stories have been omitted for the sake of clarity, this timeline covers all of the major events from the entire Halo franchise: everything from the Forerunners to Spartan Locke.
As with any retrospective, there are plenty of spoilers ahead — if you haven't gotten a chance to play through the story yet and don't want the endings of each game (not including Halo 5) spoiled, proceed with caution.
So, without any further adieu, here's the complete Halo series timeline!
Pre-Halo: Combat Evolved
• The Forerunners, an ancient race of space-faring scientists, make first contact with a parasitic organism known as the Flood. The Flood-Forerunner war begins.
• After 300 years of fighting, the Flood has conquered much of the galaxy. As a last resort, the Forerunners fire the Halo rings, a series of weapons designed to wipe out all sentient life, denying the Flood of its food source. Both the Forerunners and the Flood are annihilated.
• The Sangheili (Elites) and the San 'Shyuum (Prophets) put an end to years of fighting to form the Covenant. They begin their hunt for Forerunner artifacts, as well as absorbing other species into their massive war machine. These include the Grunts, the Jackals, the Hunters, the Drones and the Brutes.
• The United Nations Space Command, or UNSC, is formed as a militarized, exploratory division of Earth's government.
• Humanity discovers slipspace, allowing for the development of the "Slipspace drive" and faster-than-light travel.
• The ORION Project, a secret bio-engineering experiment, is green-lit. While it shows promise, the ORION project is ultimately deemed a failure.
• Humanity begins colonizing Reach, a planet that would eventually become one of the UNSC's largest military research bases.
• The ORION Project is re-initiated. The first successful batch of augmentees are code-named "SPARTANs."
• The ORION is shuttered yet again due to mental issues caused by the project's biological augmentations. Most SPARTAN-Is remain active.
• A young boy named John is born.
• Using research from the ORION Project as a stepping stone, Dr. Catherine Halsey greenlights the SPARTAN-II Project. Potential SPARTAN candidates, all of whom are children, are kidnapped and replaced with clones before being brought to Reach for training.
• The SPARTAN-IIs undergo biological augmentation. Of the original 75 candidates, only 33 survive the augmentation process and remain active.
• Humanity makes first contact with the Covenant on an agricultural colony named Harvest.
• A revolutionary exoskeleton system, named the Mjolnir Mk. IV, is developed. It becomes the SPARTAN-II's standard equipment.
• The SPARTAN-III Project, designed to produce cheaper, disposable Spartan soldiers, begins in secret.
• The Cole Protocol is established in order to prevent the Covenant from finding Earth. If capture is inevitable, captains must destroy their ship's A.I. and self-destruct.
• Office of Naval Intelligence publicly reveals the SPARTAN-IIs in order to boost morale.
• Cortana, a revolutionary A.I. system, is created from Catherine Halsey's cloned brain.
• The Mjolnir Mk. V armor, complete with reverse-engineered energy shields, is developed and adopted by the surviving SPARTAN-IIs.
• Commander Jacob Keyes defeats a Covenant fleet orbiting a human colony. However, the Covenant plant a tracking beacon on Keyes' ship and discover the location of Reach.
The Events of Halo: Reach
• Days later, a squad of SPARTAN-IIIs dubbed "Noble Team" discover Covenant reconnaissance squads on Reach. Sixty percent of the entire UNSC fleet is redirected to Reach in response.
• Despite heavy UNSC resistance, the Covenant are able to capture most of Reach within days of arriving.
• John-117, now known as the Master Chief, is introduced to Cortana. They are separated when the Master Chief leaves to defend the UNSC Pillar of Autumn, while Cortana stays behind to work with Dr. Halsey.
• Dr. Halsey learns of the true nature behind the SPARTAN-IIIs.
• Noble Team arrives to save Halsey and are ordered to bring Cortana to a ship-breaking facility and rendezvous with the Pillar of Autumn.
• Save for a single SPARTAN-III, Noble Team is killed while transporting and defending the Pillar of Autumn. Cortana successfully makes it aboard and reunites with the Master Chief.
• Cortana then provides Captain Keyes with a set of coordinates given to her by Halsey. After jumping to slipspace, the Pillar of Autumn arrives at a massive, ring-shaped facility.
The Events of Halo: Combat Evolved
• After arriving at Halo, the Chief and Cortana escape via lifeboat. Keyes crash-lands the Pillar of Autumn into Halo.
• On Halo, Chief and Cortana reunite with the surviving marines before rescuing Keyes from the Covenant.
• The group decides to split up, with the Chief searching for Halo's control room while Keyes investigates a supposed Covenant weapons cache.
• Master Chief finds the control room, only for Cortana to send him to stop Keyes. The Chief is too late, and learns of the Flood.
• After fighting his way through the Flood, the Chief meets 343 Guilty Spark, Halo's A.I. monitor. Guilty Spark promises to help the Chief wipe out the Flood by activating Halo, but Cortana reveals that this would wipe out all life in the galaxy.
• Guilty Spark turns on the Chief once the activation is halted. Cortana and the Chief escape and plan to destroy Halo by detonating the Pillar of Autumn's reactor.
• After killing a Flood-infected Keyes, the Chief and Cortana are able to destroy the Pillar of Autumn and Halo along with it. The local Flood infestation and most of the Covenant fleet are wiped out in the ensuing explosion.
The Events of Halo: First Strike
• The Master Chief and Cortana rendezvous with survivors from Halo's explosion. Together, they hijack a Covenant carrier and head back to Reach.
• On Reach, the Chief finds the few remaining SPARTAN-IIs and Catherine Halsey. They retreat to the captured Covenant vessel and flee the system.
• The group discovers that the Covenant knows of Earth's location, and find one of the largest fleets ever recorded preparing to attack. The Chief and Cortana plan a counterattack, while Halsey absconds with Kelly-087.
• Despite losing one of the SPARTAN-IIs, the Chief manages to destroy the fleet. The survivors, having delayed the Covenant invasion, head back to Earth to warn the UNSC of the impending attack.
• Also, there's something about a time-shifting crystal ... but considering the rest of the series ignores it, we will, too.
The Events of Halo 2
• While the Master Chief is being honored as a hero on Earth, the Covenant fleet commander who oversaw the destruction of Halo is deemed a heretic.
• The Covenant fleet arrives at Earth.
• The Chief manages to slow the Covenant advance until one of the Prophets initiates a slipspace jump in-atmosphere. Master Chief and a single ship are able to follow, but much of the city of New Mombasa is destroyed in the resulting blast.
The events depicted in Halo 3: ODST begin here.
• A squad of Orbital Drop Shock Troopers deploys into New Mombasa as the Prophet warps into slipspace. The squad is scattered by the shockwave.
• After regrouping underneath New Mombasa, the squad discovers a Covenant Engineer trying to defect to the UNSC. They successfully rescue it and manage to escape the city.
Halo 2 resumes.
• The Covenant fleet commander is pardoned and dubbed the Arbiter. His first task as the "Blade of the Prophets" is to assassinate a heretic leader.
• The Arbiter succeeds in killing the heretic leader, only to learn that 343 Guilty Spark had inadvertently been behind the heretic's revolt.
• Master Chief arrives at Delta Halo, and after fighting through Covenant forces, manages to kill the Prophet of Regret. The Chief is thrown into the ocean by a retaliatory orbital bombardment and is pulled under the surface.
• The Arbiter arrives at Delta Halo and manages to find the installation's firing trigger before being betrayed by the Brutes.
• Both the Arbiter and the Chief are saved by the Gravemind, a massive Flood intelligence. They agree to work together to keep Delta Halo from firing, and they split up.
• As a result of the Brutes being promoted to the Prophets' elite guards, the Elites secede from the Covenant and a civil war begins.
• Dr. Halsey and Kelly-087 arrive at Onyx, a Forerunner Shield world. After reuniting with a group of SPARTAN-IIIs, the survivors are trapped within the core of the planet.
• Master Chief is sent aboard a massive Covenant space station and proceeds to chase down the Prophets. He manages to board the Prophets' vessel, the Dreadnaught, before it escapes, but is forced to leave Cortana behind.
• The Arbiter is sent back to the surface of Delta Halo to stop the Brutes from activating the ring. He is successful, but all Halo installations are left on stand-by.
• Both the Prophets and the Master Chief arrive back to Earth.
• The rescued Engineer from Halo 3: ODST reveals why the Covenant is attacking Earth: a massive Forerunner artifact is buried beneath the planet's surface.
The Events of Halo 3
• After escaping Covenant capture aboard the Dreadnaught, Master Chief returns to Earth using a piece of the hull as a heat shield.
• The UNSC recovers the Chief. After escaping a Covenant ambush, Master Chief leads an assault that allows the UNSC fleet to attack the Dreadnaught.
• Before the UNSC can take the Prophets down, the Covenant opens a Forerunner portal and warps away from Earth.
• The Flood arrives on Earth via an infected Covenant carrier. The Master Chief is able to contain it long enough to allow the Elites to purge the infestation.
• After discovering a message from Cortana, the Chief decides to follow the Prophets through the portal. He arrives at Installation 00, otherwise known as the Ark.
• The Chief fights through both Covenant and Flood armies. He and the Arbiter manage to stop the Prophet of Truth from activating the entire Halo array, and the Covenant fleet is wiped out.
• They then discover a "replacement Halo" (based on the one that was destroyed in Combat Evolved) being constructed aboard the Ark. As the ring is still unfinished, firing it would not trigger the other Halo installations, and Master Chief decides to use this exploit to finish off the Flood once and for all.
• In order to use the new Halo, the Chief rescues Cortana from the center of the Flood infection. They then travel to the control room, and after a brief skirmish with 343 Guilty Spark, Master Chief manages to activate Halo.
• Halo fires and begins to tear itself apart. Master Chief, Cortana and the Arbiter survive the detonation, but during their escape through the portal back to Earth, the ship is cut in half. The Arbiter returns home, while the Chief and Cortana are left drifting.
• Following the war against the Covenant, the SPARTAN-IV Program is greenlit.
• Halsey and a small group of survivors are rescued from Onyx's core. The UNSC immediately arrests Halsey.
• The UNSC Infinity is officially commissioned.
The Events of Halo 4
• Cortana wakes the Chief from his cryosleep after their ship reaches a Forerunner planet named Requiem.
• After a brief firefight, the Chief, Cortana and local Covenant forces are pulled inside the planet.
• Once inside, Cortana broadcasts a distress signal, which is picked up by the UNSC Infinity.
• Cortana reveals that she is suffering from "rampancy," a condition in which A.I. "think themselves to death."
• Master Chief inadvertently awakens the Didact, an ancient Forerunner war criminal. The Didact takes control of the Covenant forces on Requiem.
• The Infinity arrives at Requiem and is pulled inside the planet's core. After the ship crashes, Master Chief finally reunites with the UNSC.
• Cortana and the Chief attempt to free the Infinity from Requiem's core. Along the way, the Chief meets with the Librarian, an ancient Forerunner scientist. She reveals the Didact's greatest weapon, the Composer, which he used to turn ancient humans into psychotic artificial intelligences.
• The Librarian alters the Chief's genetic makeup, immunizing him to the Composer's effects.
• Following another firefight, Infinity is freed from Requiem's core. The Chief stays behind (against orders) to stop the Didact.
• The Chief fails to stop the Didact from leaving Requiem and follows him to Gamma Halo.
• After retrieving the Composer, the Didact wipes out the UNSC research team at Gamma Halo. Master Chief and Cortana are the only survivors.
• The Didact heads to Earth, and the Chief follows. He and Cortana manage to infiltrate the Didact's ship.
• Master Chief manages to knock the Didact into the Composer and detonates a nuclear warhead, destroying the weapon.
• The Chief survives thanks to a hard-light shield created by a fully-rampant Cortana. After saying goodbye, Cortana dies.
• Months after losing Cortana, the Master Chief reunites with a squad of SPARTAN-IIs nicknamed "Blue Team." Together, they defeat the Didact yet again, who had survived his fall into the Composer.
• The Infinity returns to Requiem in order to clean up the remaining Covenant threat.
• Halsey is brought to Infinity to help the UNSC's research efforts but is ultimately captured by the Covenant. She discovers a Forerunner "map" that details the location of all Forerunner technology in the galaxy.
• The SPARTAN-IVs on Infinity are ordered to execute Halsey. Despite being shot, Halsey survives and remains in Covenant captivity.
• Covenant leaders activate Requiem's fail-safe, which sets the planet on a collision course with its sun. The Infinity barely manages to escape.
The Events of Halo 5: Guardians
• Details are fuzzy, but reports claim that the Master Chief and Blue Team are responsible for Forerunner attacks on human colonies.
• The Master Chief is declared a traitor, and Fireteam Osiris is formed to take him down.
As you can see, there's quite a bit of history behind Halo — and it's only going to get bigger when Halo 5: Guardians releases on Oct. 27.