The Forerunners sent the humans to Earth, reverting them to a primitive civilization based in Africa, and fought the Flood, which spread through an infestation of sentient life and overran much of the Milky Way Galaxy.

Exhausting all other strategies, the Forerunners conceived the Halo Array— ring-shaped megastructures and weapons of last resort that would destroy all sentient life in the galaxy to stop the Flood.

A civil war began between the Forerunners' commander, known as the Ur-Didact, who wanted to assimilate all the humans on Earth into his army as AIs, thus immune to the Flood, and his wife, the Librarian, who created the Ark, an instrument that was to shelter sentient species outside the galaxy and allow for the mass creation of Halo installations which could all be activated simultaneously.

The disgraced former Covenant Sangheili commander known as the Arbiter, along with many of his species, helps the humans stop the Prophet of Truth from activating the Halo Array via the Ark.

[12] While Halo had not been intended as a franchise, the Bungie team wanted to make an ambitious sequel, looking to story and gameplay ideas that had been ultimately cut from Combat Evolved, and inspired by how fans had received the game.

[13] Halo 2, was announced on August 8, 2002, at Microsoft's X02 press event,[14] and an impressive demo of the game was shown at Electronic Entertainment Expo the following year.

The demo showed off new features like dual-wielding weapons and hijacking enemy vehicles, but behind the scenes the game was undergoing a troubled development; Bungie had to scrap the ambitious graphics engine as it would not run effectively on the Xbox hardware, leadership changes resulted in more infighting, and artists and designers wasted time developing assets that would ultimately not ship in the game.

[citation needed] Part of the marketing took the form of an alternative reality game, I Love Bees, centered around a website apparently hacked by a mysterious intelligence.

In addition to shipping with the complete Halo 3 multiplayer, ODST also added a cooperative survival mode called Firefight, where players fight against waves of enemies with limited lives.

[citation needed] Halo 3: ODST released September 22, 2009, and was positively received, though its price as a full game, rather than a cheaper expansion, was occasionally criticized.

[5] The step backwards in the timeline was mirrored by the gameplay, which Bungie wanted to harken to Combat Evolved with more open environments and exploration, and the return of health packs.

[29]: 28:22 While 343 Industries worked with Bungie on ODST and Reach, the new company's first game project was Halo: Combat Evolved Anniversary, a remaster of the franchise's debut title.

[38][39] 343 Industries began staffing up their studio while beginning development on the next major Halo title, eventually growing to nearly 200,[40] and decided where they wanted to take Master Chief's story over the course of future games.

Ryan Payton was initially offered the role of creative director, but his ideas for the game did not mesh with the expected first-person shooter focus, and before prototyping was done Payon was replaced and ultimately left in 2011.

[50] The game takes place across many worlds, mainly the Elite homeworld, and revolves around Spartan Locke's hunt for the rogue Master Chief, who is trying to find a still-living Cortana.

[citation needed] The game received generally positive reviews from critics,[56] and sold an estimated 2.6 million units, a massive success for the genre on consoles.

[61] Fireteam Raven takes place during the events of Halo: Combat Evolved and puts the players in control of up to four ODST Members battling Covenant forces and the Flood within 6 levels.

To be developed by film director Peter Jackson's Wingnut Interactive, it was canceled as part of budget cuts tied to job layoffs in January 2009.

[83] Inspired by friends placing bets on their Halo matches, Mike Sepso and Sundance DiGiovanni formed Major League Gaming the same year.

GameSpot's Jeff Gerstmann described Forge as "an extremely powerful addition that might just take over your life", and praised the editor for the replay value it provided.

Grifball, a fictional sport that originated in the Halo-themed web series Red vs. Blue, inspired a popular user-created Forge map and game mode styled after rugby.

Approached by Bungie to produce something ancient and mysterious for Halo's debut, O'Donnell decided to use Gregorian chant, joining in with others to sing the vocal parts.

[citation needed] For Halo 3, O'Donnell noted he wanted to bring back the themes from the original game to help tie together the end of the trilogy.

In addition to synthesized and orchestral components, the composer focused on the choir and piano as essential elements, feeling these were important in creating the "Halo sound".

Neil Davidge served as an out-of-house composer for 343 Industries which proved to be very expensive leading Kazuma Jinnouchi to take over the responsibility of music production for Halo 5: Guardians.

[citation needed] Other novels have been written by Joseph Staten (Contact Harvest), Tobias S. Buckell, Karen Traviss, Greg Bear (The Forerunner Saga), Matt Forbeck, John Shirley, Troy Denning, Cassandra Rose Clarke, and Kelly Gay.

[115] Fred Van Lente's series, Halo: Blood Line, revolves around a black ops team of Spartan supersoldiers assigned to the UNSC Office of Naval Intelligence,[116] and debuted in December 2009.

The series' plot, occurring in the early days of the Human-Covenant War, revolves around Thomas Lasky, a young cadet at Corbulo Academy of Military Science, and how John-117 inspired him to eventually become a leader.

The feature introduces a new character to the franchise, Agent Jameson Locke, played by actor Mike Colter; Nightfall is considered to be his origin story.

[177][178] Other machinima series include Arby ‘n the Chief, Fire Team Charlie, The Codex, and the in-game interview show This Spartan Life.