Half-Life and Portal universe

Half-Life is a science fiction first-person shooter that first came out in 1998 on PC. Since then there have been many demos, mods (modifications), expansions, and even deleted concepts, NPCs and levels. Many of the games and expansions were developed by the Valve Corporation and published by Sierra Studios. However, some of the expansions were developed by Gearbox Software. In 2005, Electronic Arts took over distribution of the Half-Life series. Since the series’ first release, it has been introduced to consoles such as PlayStation 2, PlayStation 3, and Xbox 360.

The protagonist of the series is Gordon Freeman, a Black Mesa employee. In the canon expansions and spin-offs, the featured playable characters are not Gordon Freeman.

Plot
The Half-Life series begins in the 2000s, at the Black Mesa Research Facility in New Mexico. Gordon Freeman, a recently employed theoretical physicist for Black Mesa, is involved in an experiment analyzing an unknown crystal. But, when the crystal contacts with the analyzing equipment, it opens a dimensional rift between Black Mesa and another universe, causing Xen aliens to enter Black Mesa and murder much of the personnel. Black Mesa personnel attempt to close the rift, but after numerous attempts, the US Marines are sent in to kill all personnel. Freeman fights through the facility to meet with several other scientists, who decide to travel to the alien dimension, Xen, to stop the aliens. On Xen, Freeman eliminates the alien leader, Nihilanth, and is confronted by the G-Man, who offers Freeman employment before putting him into stasis. Back in Black Mesa, a second alien race begins an invasion, but is stopped when a Marine corporal, Adrian Shephard, collapses their portal into the facility. The G-Man then destroys Black Mesa with a nuclear warhead, and detains Shephard in stasis.

Nearly twenty years later, the G-Man brings Freeman out of stasis and places him onto an Earth ruled by the Combine, a alien race that used the dimensional rift caused at Black Mesa to conquer Earth. In City 17, Freeman meets surviving members of the Black Mesa incident, including Isaac Kleiner, Barney Calhoun, Eli Vance and his daughter Alyx Vance, and aids in the human resistance against the Combine. The Xen aliens, the Vortigaunts, who have also been enslaved, assist theResistance. When Freeman's presence is made known to former Black Mesa administrator and Combine spokesman Wallace Breen, Freeman becomes a target for the Combine. Eventually, Freeman sparks a full revolution amongst the human citizens. Eli Vance and his daughter are subsequently captured by the Combine, and Freeman helps the resistance forces attack the Combine's Citadel to rescue them. Breen attempts to flee in a teleporter, but is killed when Freeman destroys the dark energy reactor at the Citadel's top. The G-Man then arrives to extract Freeman before he is engulfed in the explosion, but is interrupted when Vortigaunts liberate Freeman from stasis and place both him and Alyx Vance at the bottom of the Citadel. The two then attempt to stabilize the Combine's primary reactor while the citizens evacuate the city, discovering that the Combine is attempting to destroy the reactor to call for reinforcements from the Combine's native dimension. After downloading critical data, they move through the war-torn city to the train station to take the last train out of the city. The Combine then destroys the reactor and thus both the Citadel and the city; the resulting explosion of which causes the train to derail.

Freeman awakens in one of the wrecked train cars with Alyx outside, where a forming super portal is visible from where the Citadel used to stand. They begin a journey through White Forest to a resistance-controlled missile base in the nearby mountains. Along the way, Freeman and Alyx are ambushed and Alyx is severely injured. However, a group of Vortigaunts are able to heal her. They are able to reach the resistance base and deliver the data, which contains the codes to destroy the portal as well as information on the Borealis, an enigmatic research vessel operated by Black Mesa's rival, Aperture Science. The base then launches a satellite that is able to shut down the super portal, cutting off the Combine from outside assistance. However, as Alyx and Freeman prepare to travel to the Arctic and investigate the Borealis, they are attacked by Combine Advisors, who kill Eli Vance before being driven off.

Recurring themes
Apart from the classic first-person shooter themes such as running in corridors, pushing buttons and turning into a "one-man army", the Half-Life series include many recurring themes. Although not seen in every game of the series, they include:


 * The use of trains, since most of the games of the series start on a train.
 * Vents. The player must crawl into vents many times to reach places unreachable by the conventional way. They are dark and filled with Headcrabs most of the time.
 * The mysterious G-Man always seem to oversee the game events.
 * Headcrabs and Zombies.
 * The Lambda logo.
 * Teleportation.

Retcons
Several retcons have been made since the first game's release, because it is still being written as of today (April 2009), because technological limitations have changed in the intervening time and because the sequel, Half-Life 2, was not planned until after the first game's release. These retcons include:

Characters

 * The black scientist model being the base for character Eli Vance. In Half-Life the scientists are generic NPCs with only a few variations. Later, Valve developed some of these NPC types into actual characters. Eli Vance is said to have lived at the Black Mesa facility with his wife and daughter, although they are not seen or mentioned in Half-Life, while Eli is seen twice at the start of Half-Life.
 * The bald scientist model wearing thick framed glasses being the base for character Isaac Kleiner. Although it is still unknown if he is seen in Half-Life as a real character, a scene in Half-Life shows such a scientist wielding a shotgun mirrors a Half-Life 2 scene in which Kleiner does the same.
 * The generic "Barney" security guard model being the base for the Half-Life 2 character Barney Calhoun. Barney is established as an actual character in Blue-Shift, in which he is the silent protagonist, and later in Half-Life 2. In Blue-Shift, it is established that the Barney Calhoun is the one seen pounding on a door in the transit system by Gordon Freeman at the start of Half-Life.
 * Barney says at the beginning of Half-Life 2 that he owns Gordon a beer. This being one of the random security guard phrases said in Half-Life, it is now implied that Barney actually said that at least once to Gordon back then.
 * The Black Mesa Administrator's identity as Wallace Breen and his influence on the Black Mesa Incident was not precisely defined yet at the time of the first game's release. Alyx asks Gordon at the start of Half-Life 2 if he remembers the old administrator while is he not seen in Half-Life.
 * The scientist having his meal exploded by the player in the microwave oven and the scientist saying "Gordon doesn't need to hear all this" at the start of Half-Life being merged into Episode Two character Arne Magnusson.
 * Several members of the Black Mesa team posed for a picture in the Black Mesa entrance hall, which was taken before the Black Mesa Incident. It features Gordon, Breen, three unknown scientists, and the four scientist models, two of which who made their way into real characters so far.
 * The name Vortigaunt was first mentioned in Half-Life 2. In Half-Life, Vortigaunts were known only as "Alien Slaves".
 * If the G-Man's real schemes, identity and nature are revealed in Episode Three, they were likely not defined yet at the time of the first game's release.

Misc

 * The Combine being involved in the events of Half-Life. Even though some entity was behind the Nihilanth actions, it was not defined as precisely as it is today.
 * Vortigaunts are familiar with Antlions and were in contact with them on Xen, while they are not seen in Half-Life and its expansions.
 * The timespan between Half-Life and Half-Life 2 was originally of 10 years, which was subsequently changed to 20 years at the time of Episode One’s release.
 * Chumtoads and yellow Boids being cut from Half-Life and brought back in the Gearbox expansions.

Games
The Half-Life series has core titles which carry the storyline. The games made in chronological order, portray either the events of one game or a perspective of a different character. As of December 2008, the main series consists of the original video game and its sequel, as well as three expansion packs and two episodic games. A third episodic game remains in development. In addition, several spin-off titles have been released.

GoldSrc games
Half-Life is the first title for the series, and was the debut title of Valve Software. First released on November 19, 1998, Half-Life follows Gordon Freeman, a theoretical physicist, after the Black Mesa Research Facility accidentally causes a dimensional rift which allows the facility to be invaded by aliens. Freeman attempts to survive the slaughter and resolve the situation. The game was originally published by Sierra Studios and released for Windows, although Gearbox Software would later port the game to PlayStation 2 in 2001. Valve themselves later converted the game to utilize their Source engine. Half-Life received critical acclaim upon release, critics hailing its overall presentation and numerous scripted sequences. The game won over 50 Game of the Year awards and its game play has influenced first-person shooters for years to come. Half-Life has since been regarded as one of the greatest games of all time.

Half-Life was followed by an expansion pack, Half-Life: Opposing Force, on November 1, 1999. Unlike Half-Life, Opposing Force was developed by Gearbox Software, although it was still published by Sierra Studios. Opposing Force was first announced as a mission pack for Half-Life in April 1999, and was released for the Windows version of the game. The player no longer assumes the role of Gordon Freeman, but rather sees the later events of the first game from the perspective of a US Marine corporal, Adrian Shephard. Shephard is initially assigned to cover up the events at Black Mesa, but is soon left isolated and has to fight to survive against a new group of alien invaders and black operations units. Opposing Force was received favorably by critics, many citing the game as being as influential on setting expansion pack standards as the original game had been in influencing the overall genre. The game won the Computer Game of the Year Interactive Achievement Award of 2000 from the Academy of Interactive Arts & Sciences.

Gearbox later went on to develop Half-Life: Blue Shift, Half-Life’s second expansion pack. Announced in 2000, the game was initially developed as an add-on for a Sega Dreamcast port of Half-Life; however, the port was canceled and Blue Shift was instead released for Windows on June 12, 2001. Blue Shift puts the player in the position of Barney Calhoun, a security guard working at Black Mesa. The game takes place within the early parts of Half-Life, with Calhoun attempting to escape the facility with a small group of scientists. Blue Shift also includes a High Definition pack, which upgrades the quality of the models and textures in both Blue Shift and the preceding games in the series. Critics gave Blue Shift a mixed but favorable reception, praising the game's atmosphere and the inclusion of the High Definition pack, but criticizing the otherwise lack of new content and short length of the story.

The third and final expansion for Half-Life was Half-Life: Decay. The game was again developed by Gearbox and published by Sierra. However, unlike previous titles, Decay is only available with the PlayStation 2 version of Half-Life. Decay is unique within the Half-Life series as the only cooperative game. Decay focuses on two of Freeman's colleagues, Gina Cross and Colette Green, as the two work with other scientists to counter the effects of the dimensional rift and ultimately attempt to close it. Released on November 14, 2001, Decay received a weak but overall positive reception from critics, many reviewers stating that it was fun to play through with a friend, but that the game's more puzzle-orientated game play detracted from the overall experience. An unofficial Windows port of the game was released in September 2008.

Source games
On November 16, 2004, Valve released Half-Life 2, the sequel to the original game. The game had a six year development cycle, which saw several delays and the leak of the game's source code. Half-Life 2 returns the player to the role of Gordon Freeman, now employed by the G-Man. Set twenty years after the original game, has been occupied by the Combine, an alien race that exploited the events of the first game to invade. The G-Man inserts Freeman into City 17 to combat the Combine occupation. Half-Life 2 acquired near-unanimous positive reviews and received critical acclaim, winning over 35 Game of the Year awards for 2004. The game has been critically praised for its advances in computer animation, sound, narration, computer graphics, artificial intelligence, and physics. Half-Life 2 was the first title to use Valve's Steam content delivery system, a system that eventually led to Valve falling out with publisher Sierra Entertainment.

Following Half-Life 2, the series was continued using a trilogy of episodic games. Half-Life 2: Episode One was the first of these, set around City 17 after the events of the original game, in which Freeman and Alyx Vance must attempt to escape the city after a dark energy reactor core they damaged at the end of Half-Life 2 threatens to destroy the city. Developed by Valve, the game was distributed online via Steam and through retail by Electronic Arts. It was released on June 1, 2006, and introduced several new graphical effects including new lighting features and facial animation. Episode One received a generally positive critical reaction, although the game's short length was a point of common criticism.

The second episodic game, Half-Life 2: Episode Two, continues the story from where Episode One ended. It was released on October 10, 2007, bundled with the games Portal and Team Fortress 2 as well as Half-Life 2 and Episode One in the package The Orange Box, which was released for Windows PCs, the Xbox 360, and PlayStation 3 consoles. The game was again developed by Valve, and distributed using both Steam and Electronic Arts. Continuing with Valve's policy of orienting each episode around a particular theme or set of technologies, Episode Two focuses on expansive environments, travel and less linear play. As Gordon Freeman, the player travels with Alyx Vance away from the ruins of City 17 into the surrounding countryside, pursued by Combine forces. Episode Two's new technologies and game play features were praised by reviewers; however, the short length of the game was again a point of criticism.

Half-Life 2: Episode Three is the third and final installment of the episodic expansions developed by Valve Corporation. It is planned as the last episode in the currently planned story arc, although not necessarily the end of the Half-Life franchise. According to Valve, plot details have not been finalized as of February 2008, and the game is also not expected to be released for some time. The game did not appear at E3 2008, but some concept art has surfaced.

Spin-offs
The success of the Half-Life series has spurred the creation of several spin-off games for Half-Life 2. Codename: Gordon is a two-dimensional Flash sidescroller shooter produced by Nuclearvision Entertainment, and was released over Valve's Steam online delivery system on May 17, 2004, as a promotional game for the, at that time, upcoming Half-Life 2. Presently, the game is unavailable on Steam due to its developer's bankruptcy, causing their official site to go offline. Codename: Gordon was well received by reviewers and the public, and attracted over 600,000 players in the first three weeks after its release. Reviewers praised the game for its game play and unique dialog style, but also criticized it for its improper optimization, and lack of opponent variety.

Half-Life 2: Lost Coast is a technology demonstration, developed by Valve to display new high dynamic range rendering and a variety of other features. The level was designed with a variety of appropriate environments to emphasize these effects. Consisting of a single map, Lost Coast was originally to be part of Half-Life 2, but was dropped during development. The game follows Gordon Freeman as he travels up a coastal cliff to destroy a Combine artillery launcher in a monastery, which is firing on a nearby town. Released over Steam on October 27, 2005, the level received a generally positive reception, and there was consensus among reviewers that the new features should be implemented into future games released by Valve.

Portal is a puzzle game set in the Half-Life universe, developed by Valve Corporation. It was initially released alongside Episode Two in The Orange Box on October 10, 2007. The player controls a female test subject named Chell as she moves through the laboratories of Black Mesa's primary rival, Aperture Science, completing various tests with a device that allows her to create linked portals in physical space. In the later stages of the game, the player battles GLaDOS, a corrupt artificial intelligence computer that monitors her every move. The game is the spiritual successor to Narbacular Drop, with many of the same team members working on the game. Portal has been acclaimed as one of the most original games in 2007 despite being comparatively short in length, receiving praise for its unique game play and darkly humorous story. An Xbox Live Arcade expansion was released on October 22, 2008, whilst a sequel to Portal has also been confirmed.

Development
The video game development company behind the Half-Life series, Valve Corporation, was founded in 1996 in Kirkland, Washington by former Microsoft employees Mike Harrington and Gabe Newell. They began working on the first game of the series soon after the company's formation, and settled on a concept for a horror-themed 3D action game, using the Quake engine as licensed by id Software. The game was a hit at the 1997 E3 convention, where its animation system and artificial intelligence were demonstrated. The game's success led to its first expansion pack, Half-Life: Opposing Force, which was developed by Gearbox Software, a company based in Plano, Texas, and announced on April 15, 1999. Randy Pitchford, founder of Gearbox, said in an interview that he believed Valve gave them the opportunity to produce a sequel to Half-Life to allow Valve to focus on future titles. The game was demonstrated at the 1999 E3 convention, where new locations, characters, and the story were revealed.

The second Half-Life expansion pack, Half-Life: Blue Shift, was again developed by Gearbox Software and announced by its publisher, Sierra Entertainment, on August 30, 2000. The game's story and development direction were first revealed at the European Computer Trade Show in September 2000.

Impact of Half-Life
A short film based upon Half-Life, titled Half-Life: Uplink, was developed by Cruise Control, a British marketing agency, and released on March 15, 1999. However, Sierra withdrew it from circulation, after Cruise Control and Valve had failed to resolve licensing issues with Cruise Control over the film. The critical reception of the film was very poor. The film's plot was that of a journalist attempting to infiltrate the Black Mesa Research Facility and discover what has happened there.

In early 2009, the Purchase Brothers, a Toronto-based film company, released a five-minute film based on Half Life 2 called Half-Life: Escape from City-17. The film combines live-action footage with 3D animation created using the Source SDK for the video game.