Doom 3 (stylized as DOOM³) is a 2004 survival horror first-person shooter video game developed by id Software and published by Activision. Doom 3 was originally released for Microsoft Windows on August 3, 2004, adapted for Linux later that year, and ported by Aspyr Media for Mac OS X in 2005. Developer Vicarious Visions ported the game to the Xbox, releasing it on April 3, 2005.
Doom 3 is set on Mars in 2145, where a military-industrial conglomerate has set up a scientific research facility into fields such as teleportation, biological research, and advanced weapons design. The teleportation experiments open a gateway to Hell, resulting in a catastrophic invasion of the Mars base by demons. The player controls a space marine who fights through the base to stop the demons attacking Mars and reaching Earth.
Doom 3 is the first reboot of the Doom series, ignoring the events of the previous games. Doom 3 utilizes the id Tech 4 game engine, which has since been licensed out to other developers, and later released under the GNU General Public License v3.0 or later in November 2011.
Doom 3 was a critical and commercial success; with more than 3.5 million copies of the game sold, it is the most successful game by developer id Software to date. Critics praised the game's graphics and presentation, although reviewers were divided by how close the gameplay was to that of the original Doom, focusing primarily on simply fighting through large numbers of enemy characters. The game was followed by Resurrection of Evil, an expansion pack developed by Nerve Software, in April 2005. A series of novelizations of Doom 3, written by Matthew J. Costello, debuted in February 2008. An expanded and remastered edition titled Doom 3: BFG Edition was released in the fourth quarter of 2012, while a version based on BFG Edition of the game was released without online multiplayer, simply called Doom 3, for Android in June 2015, and Nintendo Switch, PlayStation 4 and Xbox One in July 2019.
UAC board member Elliott Swann, his bodyguard Jack Campbell and a recently transferred Marine arrive at Mars City, the main access to the UAC's Mars base, disembarking from an Earth transport ship. Sent to investigate multiple incidents involving the Delta Complex, Swann has a tense meeting with facility’s director Dr. Malcolm Betruger while the Marine heads to Master Sergeant Thomas Kelly for orders. Kelly orders the Marine to find a scientist from the Delta Labs who has gone missing. The marine finds the scientist in a nearby decommissioned communications facility, where he is frantically trying to send a warning to the UAC on Earth about Betruger's teleportation experiments. However, as he tries to explain the situation to the marine, another teleportation test takes place but loses containment, at which point the entire Mars base is swept with an unnatural shockwave. The forces of Hell invade through the teleporter's portal and transform most of the base's personnel into zombies.
Now forced to fend off attacks from zombified base personnel and the demons from Hell, the marine returns to Mars City, where Kelly remotely gives the marine orders to link up with another squad of marines (Bravo Team) and get a transmission card containing a distress call to the main communications facility to call for reinforcements. As the marine progresses through the base, he learns that Swann and Campbell have survived, and are also en route to the communications facility to prevent any messages being sent in hope of containing the situation on Mars. The marine squad is ambushed by demons and slaughtered in the EnPro Plant, and although the marine recovers the transmission card, he is too late to prevent the bulk of equipment at the communications facility being destroyed by Campbell. However, Kelly directs the marine to a backup system, where the marine is given the choice of whether to obey Kelly's orders to send for reinforcements, or accept Swann's argument to keep Mars isolated until the exact nature of the invasion is understood, so as not to endanger Earth. The marine is told to go to the Delta Labs by Kelly or Swann, depending on whether the transmission is sent or not.
On the way to the Delta Labs, the marine is contacted by Betruger, who is now clearly shown to be working in cooperation with Hell in order to invade Earth. If the marine did not send the distress call to Earth, Betruger does so himself, hoping to use the ships bringing reinforcements to transport the demons to Earth. Betruger then unsuccessfully attempts to kill the marine using the toxic gases in the base's recycling facilities. Upon arriving at the Delta Labs, the marine learns of the details behind the teleportation experiments, expeditions into Hell to retrieve specimens and Betruger's increasing obsession with the tests, as well as of a xenoarchaeological dig under the surface of Mars. The dig is excavating the ruins of an ancient civilization discovered on Mars, and has produced a relic known as the Soul Cube. According to a scientist the marine finds alive in the labs, the Soul Cube is a weapon created by the ancient civilization to defend against the forces of Hell. The scientist also reveals that the invasion began when Betruger took the Soul Cube into the portal at the beginning of the game, depositing it in Hell. The marine pursues Betruger through the labs, but is pulled into the main teleportation portal after being lured into a trap by Betruger.
The portal takes the marine directly into Hell, where he proceeds to fight his way through the large number of demons to the Soul Cube, defeating its demonic guardian. The marine is then able to reinitialize the teleportation equipment left by research expeditions into Hell and return to the Delta Labs. Betruger, however, tells the marine that although the main UAC teleporter has been destroyed, Hell is opening a Hellmouth on Mars, capable of bringing millions of demons to Mars. The marine encounters the injured Swann further in the Delta Labs, who informs the marine that Kelly has been working with Hell for possibly the whole time, and has been transformed by the demons. Telling the marine that Campbell has gone after Kelly, Swann gives the marine his PDA containing information on the location on the Hellmouth under the surface of Mars and assures him that he will try to make his way out of the base alone.
However, when the marine catches up with Campbell in the central computer processing sector of the base, Campbell is mortally wounded and only has enough strength to say that Kelly has taken Campbell's BFG 9000 weapon before expiring. Kelly then begins to taunt the marine in a demonic voice. The marine eventually faces off with Kelly in the central computer core, revealing Kelly as a cybernetic human grafted onto a tank-like base. The marine is able to kill Kelly and takes the BFG 9000 before proceeding deeper under the Martian surface to Site 3, the archaeological dig site where the Soul Cube was unearthed. At the primary excavation site, the marine discovers the Hellmouth, defended by Hell's mightiest warrior, the Cyberdemon. Using the Soul Cube, the marine defeats the Cyberdemon in combat, and the Soul Cube then seals the Hellmouth. The ending cut scene shows the reinforcements from Earth arriving at the base to discover the carnage. They find the marine alive, but discover that Swann has died from his injuries while the marine was on his way to the Site 3. They are, however, unable to locate Betruger, who in the final scene is shown in Hell, reincarnated as a dragon-like demon.