HλLF-LIFE was a hugely influential video game, released in late 1998. Using scripted sequences, exceptional level design, crisp graphics and mechanics (by 1998 standards, obvs), etc. it changed the way stories were told in action/shooting video games.

Our main Half-Life entry is the character profile for Gordon Freeman, the protagonist. This companion story explains what happens in-game, since HλLF-LIFE and its expansions had their own mythos and storylines.

The bulk of this article well precedes later HL video games.




This timeline incorporates the events of the Opposing Force and Blue Shift expansions. However these events are not necessarily canon.

Mark Laidlaw, the head writer for the Half-Life series, stated that the expansions are “semi-canon”. While ideas and events from the expansions may be used in future games, as the nuking of the Black Mesa facility in OpFor has already been, Valve is only concerned with remaining consistent with the previous games in the main series (Half-Life, Half-Life 2 and the subsequent Episodes).

Laidlaw has further stated that his primary concern is with telling stories and providing good gameplay. Thus, Valve may change details as necessary to facilitate this. In this view, each of the games is a Rashomon -style presentation of how each protagonist experienced events and does not necessarily provide “objective” information.

This timeline should be read in a similar way — a possible interpretation of events suitable as a springboard for story ideas and background setting.

The notes in italics are out-of-universe background information.

Alien names are only capitalized the case being a specific singular entity such as Geneworm or if the name is a formal title such the Xen Controllers.



The Black Mesa Incident, also known as the Lambda Incident, refers to the dimensional incursion between Earth and Xen. It began, as so many discoveries do, with an accident.

The incident occurred at the Black Mesa Research Facility (BMRF), a decommissioned missile base located inside the Black Mesa in New Mexico. The events leading up to the incursion began with teleportation experimentation at the BMRF. It was attempting to develop the technology before their rival company Aperture Science.

The teleportation effect created by the AP labs consisted of two 1-meter-wide coronal light-spheres. There was a green departure sphere with an orange corona and an orange arrival sphere with a green corona. Contact with the departure sphere removed the target from our dimension and after a short trip (1 Phase in DC Heroes RPG terms) the target reappeared beside the arrival sphere.

Some rumored but unconfirmed side effects have included temporal transportation (i.e. time travel) and reduction of the teleported subject’s physical dimensions (a 6’ man being reduced to 1” in height — Shrinking: 10). If these events truly occurred, they were exceedingly rare.

Corridor and computers in the Black Mesa center

Given the reports of test subjects that they perceived some passage of time in a sort of limbo during the transit, it was speculated that the teleportation process involved an actual dimensional  displacement. Further experimentation resulted in a successful breach of the dimensional barriers, and the U.S. government discovered the dimension of Xen (Travel Distance 6/6).

(The rumored side-effects refer to various popular unofficial Half-Life mods. Whether these are urban legends among the BMRF staff or reflect real events is up to the GM.)

(The discovery and exploration of Xen prior to the events of Half-Life are not directly depicted in the games. But these become clear from the numerous samples of material and wildlife that had been gathered and stored in Black Mesa prior to the incursion. Furthermore, remnants of deceased survey parties, abandoned equipment and small human facilities are found throughout Xen in Half-Life and its expansions.)


Xen is a vast void, the skies of which are filled with fantastically colored nebulous clouds and a breathable atmosphere. The long-term health effects of unfiltered respiration in Xen’s atmosphere is unknown. Xen has no known planetary masses as such, but rather has floating “islands” in the sky.

Gravity in Xen is weaker than on Earth (Gravity Decrease: 02) and is always oriented in the same direction. Oddly enough, despite the consistent orientation of Xen’s gravity, the islands are somehow anchored in place.One exception is the smallest fragments (three or less meters across), which orbit the larger ones. Most islands are flat with a few small hills and grottoes.

A view of Xen

Most of the life forms are relatively benign. These consist in oddly shaped vegetation, some of which glows. There were also natural springs, which had healing effects on human beings (Regeneration: 14).

Less-benign life forms include laser crystals (BODY 02, attack anyone within 2 APs with Lightning: 04) and Xen spear-trees (BODY 10 DEX 04, Claws: 12), both of which were fortunately immobile. Barnacles and houndeyes were common and some were captured for study.

A few headcrabs were also caught. And vortigaunts and bull squids were observed from a distance.


When Gordon Freeman made his trip to Xen after the invasion of Earth, he only encountered barnacles in one isolated circumstance. On Earth, the barnacles spread themselves rapidly through the complex by unknown means, possibly through spores similar to Terran molds. Isolated areas of Black Mesa were already infested with them before the invasion.

Thus, it is speculated that the barnacles may have been planted for the science teams in order to facilitate such an infestation.

Black Mesa Anomalous Materials Lab - entrance lobby (Half Life video game)

Entrance lobby of the Black Mesa Anomalous Materials Lab before the incident.

Given that the barnacles were able to thrive without being fed regularly, it is possible that they actually metabolize atmospheric materials for survival much like Terran plants with “air roots”. If so, perhaps they only captured targets to minimize resistance to the Xen invasion. And possibly gather Terran genetic material for use in Nihilanth’s fortress/factory.

The relative scarcity of barnacles in Xen may have more mundane explanations. For instance, there may not be as many suitable surfaces for the barnacles to form on or they may have natural predators.

When initially encountered on Xen, bull squids and vortigaunts (dubbed “alien slaves” because of the metallic-green collars on their necks and wrists) were non-hostile. They went about their activities with no notice of the research teams.

It is possible that the bull squids were only hostile on Earth because of physical/psychological stress from their dimensional displacement. The vortigaunts on Xen became hostile after the Resonance Cascade as their master, the Nihilanth, had then begin active attempts to invade Earth. See the vortigaunt writeup for details.


Material samples were also gathered from Xen, and subjected to various experiments, including an Anti-Mass Spectrometer. Samples of Xen crystals placed in this device generated anomalous results.

Finally, at Noon on May 16, 200-, the purest sample of Xen crystal yet discovered was placed into the Anti-Mass Spectrometer of Section C of the Black Mesa Research Facility Anomalous Materials Laboratory.

Large experimental equipment at Black Mesa

(The year of the Resonance Cascade has been left deliberately vague in-game. But the dates and days on the calendars displayed throughout Black Mesa only correspond with two “200-” years — 2003 and 2008.)

(The OpFor expansion manual has diary entries from Corporal Shephard refers to the Resonance Cascade occurring on March 16. But the background information appearing in all of the other games and expansions indicates the date was May 16.)

Upon exposure to the energies of the Anti-Mass Spectrometer, the incident occurred. The Resonance Cascade resulting in a full-scale dimensional incursion upon Earth by Xen. Much of Black Mesa was wracked by massive explosions and quakes. The forces of Xen began teleporting into the Earth Dimension in vast numbers, albeit spread throughout the facility.

Resonance cascade in Black Mesa


The Black Mesa systems were plagued by malfunctions several hours prior to the accident. These malfunctions may have been caused by the continuous system strain from the exploration of Xen. This was a vastly equipment- and power-intensive activity. The constant dimensional transports may also have been causing collateral damage to Black Mesa.

The mysterious person dubbed the G-Man apparently suspected something would occur during the tests.Thus, he had begun personally supervising the training of the USMC Hazardous Environment Combat Unit (HECU) troops who would be sent into BMRF after the resonance cascade. Whether he actually suspected a dimensional incursion would result or if he was simply being cautious is unknown.


This first wave consisted of the following xenoforms (See the entries for more information on these aliens):

  • Hagworms.
  • Headcrabs (and by extension, the “mawmen”).
  • Barnacles (in much greater numbers than they had appeared before).
  • Houndeyes*.
  • Bull Squids*.
  • Vortigaunts a.k.a. Alien Slaves.

* These species did not seem to actually serve the Xen forces, but rather roamed wildly on their own. In fact, bull squids were actually seen to attack other Xen life forms. These life forms may have been transported to Earth by accident due to collateral fallout from the resonance cascade. Or they may have been deliberately teleported to Earth by the Nihilanth simply to harass the Black Mesa staff.

Three hours after the incident began, a second wave of larger xenoforms reinforced the first wave (See the entries for more information on these aliens):

* As with the bull squids and houndeyes in the first wave, these species did not seem to actually serve the Xen forces. Tentacles were seen to attack Xen life forms as readily as Terran ones.


In the wake of the accident, there were scattered pockets of resistance throughout Black Mesa. These efforts fell into two categories:

  1. Trying to discover what had occurred.
  2. Fortifying against the alien invaders until help arrived.

Due to an almost-complete failure of communication systems within Black Mesa, these efforts were largely uncoordinated. Yet Gordon Freeman was able to provide some leadership. Once the scope of the catastrophe became clear and the military intervention became hostile, Freeman shifted his efforts to stopping the Xen invasion.

The accident at Black Mesa so totally disrupted operations that it actually took almost two hours for the Administrator to call in the USMC HECU teams. They arrived three hours after the accident.

They were ambushed by much more powerful forces than they had anticipated, as the second alien wave was just arriving. Several of their Osprey transports  were shot down on approach by alien flyers. Their intervention quickly became a battle to survive long enough for them to regroup.

Going in

By the fifth hour the HECU troops had taken control of the surface-level facilities of Black Mesa. Howbeit, they were still engaged in sporadic fighting against Xen reinforcements. The marines were then ordered to send expeditionary forces into the underground levels of Black Mesa.

The extent of the alien invasion quickly became clear. The marines were ordered to terminate every living thing in Black Mesa, including any surviving staff. That was both to maintain secrecy and to prevent potentially contaminated personnel from escaping.

They were also ordered to capture some Black Mesa staff, particularly Gordon Freeman (the only living witness to the accident), for debriefing. Garbled communications and a general desire on the troops’ part to punish the parties responsible for this attack quickly changed this order into “Kill Freeman.”


The HECU force’s attempts to sterilize Black Mesa were ineffective. They were not heavily-equipped enough to combat such a powerful, heavily-entrenched enemy.

Furthermore, some troops balked at summarily executing civilians, particularly those forces that had actually joined with Black Mesa staff during the initial counter-assault. One example was Corporal Adrian Shephard’s team, which had been separated from the main force when they were shot down on approach. This team only survived by linking up with Black Mesa security staff.

Fighting continued into the night, albeit at a slower pace as the Terran and Xen forces rested, regrouped, and fortified their emplacements.

By morning it became clear that the USMC forces were insufficient for sterilizing BMRF. By 8 a.m. the order was given to fall back to the extraction points. As the Marines pulled out the G-Man sealed the entrances into Black Mesa, trapping anyone left behind inside. That included HECU soldiers who had not yet made it to the surface.

By 10 a.m. the extraction was complete. The marines maintained emplacements on the surface. Meanwhile black-ops troops (with no qualms about killing as many people as necessary) moved in to place a nuclear bomb inside Black Mesa.


As the Marines pulled out, reports started filtering in of a new species appearing in Black Mesa. One of these species was in fact an old one, the mawman. Many of those had been mutating long enough to reach the second stage, dubbed a Genome for reasons unknown.

Many of the new species were, in fact, from a new faction. They were given the collective name of Race-X.

The Race-X aliens were distinct in that they seldom appeared in the same place as Xen aliens. On the one observed occasion when they did, Race-X shocktroopers attacked and killed a Xen garg. Furthermore, none of the Race-X species have ever been observed in Xen, neither before nor after the accident.

The first wave of Race-X aliens only consisted of pit drones and shocktroopers. They were in groups of one species or the other or in teams of a single shocktrooper with a pair of Pit Drones.


The precise relationship between Race-X and Xen is unknown. Geneworm entered the Earth dimension from Xen. That was established when Adrian Shephard used a Displacer Gun during his battle with Geneworm and espied Geneworm caught between the two dimensions.

Geneworm shared morphological traits with other Xen species such as the barnacles. Some species of Race-X and Xen also shared a distinctive single eye and/or flagellating feelers around the mouth, but this may be coincidental.

(Stephen Bahl, the creator of Race-X for the OpFor expansion, has explained that Race-X was from a dimension beyond Xen. They also gained temporary access to Earth through the Resonance Cascade. This allowed the OpFor expansion to use some new enemies for without conflicting with the overall Half-Life plot.)


At approximately Noon, 24 hours after the initial Xen incursion, Gordon Freeman had found the Lambda Complex team. These managed Black Mesa’s dimensional gate generator to Xen. The gate equipment was damaged, but could be opened long enough to transport one person to Xen. The goal was to find the force keeping the dimensional barriers between Xen and Earth open.

Gordon Freeman was selected for the trip. This was based on his combination of scientific knowledge and demonstrated athletic ability. Freeman was the only surviving HEV-rated member of the Black Mesa staff.

Floating structures on Xen

As the gate was activated, the creatures known as Xen Controllers began teleporting into the dimensional gate chamber. They attacked the scientists running the d-gate generator in an attempt to stop the transit.

Adrian Shephard, whom had been fighting his way through Black Mesa to find a way out, arrived at the chamber as the transit took place. He helped battle the Xen Controllers long enough for Gordon to jump through the gateway — a huge transport sphere.

And thus man returned to Xen.


In the aftermath of Freeman’s transit the Xen Controllers slaughtered the remaining Black Mesa personnel in the d-gate chamber. Adrian Shephard, who had arrived at the chamber at the moment Freeman jumped to Xen, narrowly escaped through a Xen d-gate. He found another d-gate in Xen and returned in a different part of Black Mesa.

He battled on and encountered two new Race-X aliens:

  1. The Pit Worm, which he killed by exposure to toxic waste.
  2. Several groups of voltigores.

Shephard linked up with other marines that were left behind during the evacuation. They engaged the black-ops troops, who were killing anyone they encountered to prevent interference with the placement of the nuclear device.


Meanwhile, Gordon Freeman proceeded through Xen, battling its various denizens and passing through multiple transport spheres. In addition to encountering the previously-noted Xen life forms, Freeman also met with several:

  • Xen Controllers (first briefly encountered on Earth when the BMRF d-gate was opened).
  • Gonarch (who protected the entrance to Nihilanth’s Fortress/Factory ala the mythical Cerberus).
  • Baby Headcrabs (spawned by Gonarch).
  • Nihilanth.

After defeating Gonarch, Freeman gained access to the Nihilanth’s fortress/factory. There alien slaves toiled at the direction of Xen Controllers to grow alien grunts, which were decanted and held in large barrels [BODY 07].

Freeman made his way through the factory, and fought the Nihilanth in his vast control chamber. The Nihilanth had been the force keeping the dimensional barriers between Xen and Earth open. In defeating it Freeman had ended the Xen invasion.


The battle in Black Mesa did not end with Nihilanth’s defeat. Thought the Xen forces were no longer appearing, the black-ops and Race-X forces still needed to be neutralized.

Adrian Shephard and his ad-hoc marine squad killed the last of the black-ops forces, deactivated the nuclear device, and eliminated the remainder of the Race-X forces. However, Shephard’s compatriots died during those battles.

Consequently, it fell to Shephard alone to battle Geneworm, leader of the Race-X forces. Shephard ambushed Geneworm as it exited its portal, and managed to drive it out of the Earth Dimension. Geneworm’s current status is unknown.


In the wake of their battles the enigmatic G-Man separately contacted both Freeman and Shephard.

The G-Man’s conversation with Freeman implied that his employers now controlled Xen with the help of human military forces. Remnants of these could be seen throughout Xen during their talk. The G-Man offered Freeman the choice to work with him or die. Freeman agreed to work with the G-Man, only to be placed in a timeless limbo… (to be continued in Half-Life 2).

During his conversation with Shephard, the G-Man reactivated the nuclear weapon previously disabled by Shephard, destroying Black Mesa. The Administrator told Shephard that he was ordered to dispose of the Corporal, but was sparing him out of respect for his resourcefulness. Shephard was then taken to an unknown location…

By Roy Cowan and Mark Ayen.

Source of Character: Half-Life video game.