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"...what the Combine fear the most is not any tangible human weapon, but our will, our intellect, our ability to respond selectively and rationally to every terror they turn against us. We place our firmest hope in the human spirit, even knowing how easily it may be shattered."
―Isaac Kleiner[src]

Dr. Isaac Kleiner is a scientist and one of the main characters of Half-Life 2 and its episodes. An archetypal 'absent-minded genius scientist' (although somewhat more benign), he is a prolific author of several works on teleportation and interdimensional travel, and one of the few survivors of the incident that took place in the Black Mesa Research Facility. Later on, he becomes a key (if somewhat self-conscious) leader of the Resistance against the Combine, and a prime member of the Resistance science team.



Gordon letter 2

The second page of L.M.'s letter, where Kleiner is mentioned for the first time.

Kleiner first worked as a professor at MIT, where he was one of the mentors of Gordon Freeman. It appears that the two started their friendship already back then, and that Kleiner was quickly impressed by Freeman. Kleiner would later take employment in the Sector C Test Labs of the Black Mesa Research Facility, where he worked with Eli Vance and security guard Barney Calhoun.

During this time, Kleiner appears to have become a widely recognized scientist, seeing that he is on the front cover of the magazine Popular Scientist, apparently in an article called "Next level of quantum physics", as well as the author to at least one book, From Here to There in Under a Second, likely about teleportation.

When Freeman showed interest in a job at Black Mesa, Kleiner recommended him for employment in the Civilian Recruitment Division, and this recommendation combined with Freeman's experience at the Institute for Experimental Physics in Innsbruck, Austria, ensured that he got the position instead of his competitor, Judith Mossman. In Black Mesa, Kleiner would also compete for grant money with Arne Magnusson.

Popular scientist

A brown-haired Isaac Kleiner on the cover of Popular Scientist. The hair was Photoshopped on a screenshot of his model.

Kleiner appears to have been working with administrative jobs prior to the Black Mesa Incident in Sector C, as he received carbon copies of several letters, from L.M. to other employees, such as his letter regarding Barney Calhoun's new Blue Shift assignment, sent on May 9, 200-, and L.M.'s letter to Colette Green regarding the Xen crystal swap prior to the incident. Kleiner also appeared to be a Hazardous Environment Supervisor or Instructor, as the Hazard Course Training Schedule sent by Gina Cross to Colette Green mentions that Kleiner was slated to instruct Green for a Hazardous Materials Handling on May 9, 200-, although it was postponed to June.[1] At this time, Kleiner also was on friendly terms with many co-workers, namely Gordon, Eli and Barney, although Richard Keller mentions at the start of Decay that he does not understand what Kleiner sees in Freeman.

Photo group001a2

The Anomalous Materials team before the Black Mesa Incident. Kleiner is the third from the right.

When the Resonance Cascade and resulting Black Mesa Incident occurred, Kleiner managed to escape Black Mesa, although exactly how remains unexplained. After escaping the facility, Kleiner relocated to City 17, where he formed up the core of the local Resistance along with Eli Vance, Judith Mossman and Barney Calhoun. As Kleiner and Eli entered City 17, however, Eli lost his leg to a Bullsquid while helping Kleiner over a fence. In the city, Kleiner set up a small lab beneath an abandoned Northern Petrol building, and began working on teleportation, among other works, while also staying in touch with Eli and Judith, who were working at Black Mesa East in the city's outskirts, as well as Eli's daughter Alyx, who was growing up.

Barney worked as a double agent for the local Civil Protection forces at this time, while in the meantime ensuring that Kleiner's Lab would go undiscovered and safe from the Combine. At one point, Kleiner finished his teleport, and tested it with a cat, apparently resulting in its death, forcing Kleiner to resume work on it. In this time, Kleiner also found a Headcrab, which he de-beaked, making it harmless, and named it Lamarr, before keeping her as a pet and, to an extent, domesticating her, much to the disdain of Barney. When Alyx grew older, Kleiner also worked with her and Barney to rescue Citizens from the Combine, and evacuate them through the Underground Railroad located in the City 17 Canals to Black Mesa East. At the time of Half-Life 2, Kleiner is finishing up his teleport.


Half-Life 2[]

Kleiner scan

Kleiner operating a retinal scanner to open the door to the resurrected teleport.

Along with colleagues (and fellow survivors) Alyx Vance, Eli Vance and Barney Calhoun, he makes up the core of the Resistance against the Combine. Dr. Kleiner has set up a lab in City 17 in an old abandoned warehouse. A teleportation system, developed jointly by Kleiner and Vance, allows for near-instantaneous transportation between Kleiner's Lab and Vance's facility, several miles distant. As a pet, Dr. Kleiner keeps a debeaked Headcrab he calls "Lamarr". When Barney informs him that Gordon Freeman has arrived, Kleiner tells Barney to send Gordon on his way - although he forgot that Gordon would not know the way to the lab. Alyx eventually has to rescue Gordon and show him the way to the lab.

D1 trainstation 050010

Kleiner in his lab with Alyx, Barney and Gordon.

Kleiner then reintroduces Gordon to his HEV Suit which he has upgraded before sending him on his way to Black Mesa East, outside the limits of City 17. Unfortunately, Lamarr interferes with the teleportation process. Gordon is thrown through several locations, twice in Wallace Breen's office in the Citadel, Eli's lab, a lake containing Ichthyosaurs, and a desert before finally rematerializing outside the window behind Dr Kleiner. He is then required to leave Kleiner's Lab on foot and will not return until the City 17 uprising.

During the rebellion, Dog turns up to Kleiner who keeps him safe in his lab. Kleiner is apparently alone during most of the uprising (save for Lamarr) as Barney is leading on the rebellion fronts, so he protects himself with a shotgun. When Gordon and Alyx teleport in from Nova Prospekt a week into the rebellion, Kleiner is very optimistic about the Resistance's odds and tries to convince Alyx of this, at which he fails. He is not seen for the rest of the game but manages to escape City 17 at some point between when Alyx leaves to find Gordon and the start of Episode One.

A depiction of Kleiner's younger self can also be seen in the lab, appearing on the cover of Popular Scientist, a fictional magazine (and spoof of Popular Science magazine). In it, he sports sideburns and has more hair, which is seen as brown in color. Although this is a somewhat 1970s/80s look, the picture likely dates from around the Black Mesa Incident, thus in the mid to late 1990s. Below the magazine cover is a young Alyx's drawing of him, with the affectionate words 'Uncle Kleiner' on it. A book by Kleiner, From Here to There in Under a Second (likely about teleportation), can also be found in Eli's lab at Black Mesa East.

Half-Life 2: Episode One[]

Alyx kleinercast

Alyx listening to Kleiner's Breencast.

In Half-Life 2: Episode One Kleiner is not seen in person and is only spoken to directly once in a video transmission with Alyx during the first chapter. However, he is frequently seen during the later chapters on video screens and televisions previously reserved for Breencasts. This message is recorded and looped, simply instructing survivors to make their way to the nearest train station to evacuate City 17. Kleiner also amusingly informs people that the Combine's Suppression Field is no longer in effect so that "those so inclined should give serious consideration to doing their part for the revival of the species" to which Alyx comments, "is Dr Kleiner really telling everyone to... get busy?". The messages also include some vague information to try and rally people in the face of the fact that the Rebellion is only really beginning and will likely get worse before it gets better. It is likely that all these transmissions are broadcast from White Forest.

Half-Life 2: Episode Two[]


Kleiner, Eli and Alyx talking about the Borealis at White Forest.

Kleiner reappears once again in Half-Life 2: Episode Two. First, he is seen beside Dr. Eli Vance and Dr. Arne Magnusson on the first video communication with Alyx and Gordon; he is not seen again until later on when Alyx and Gordon reach White Forest (except during the G-Man's speech). He spends most of his time working with Dr. Magnusson on his rocket. Before the launch, Kleiner briefly notes that there is an eight and a half pound anomaly, but Magnusson declares it is within tolerance and the rocket should be fired anyway. Unfortunately for Kleiner, the anomaly was Lamarr who had snuck onto the rocket while the nose cap was open earlier.

Towards the game's ending, when it is discovered that Judith Mossman found the Borealis, Kleiner is enthusiastic about the research contained on the vessel's use against the Combine, but Eli disagrees and states it could be responsible for another disaster on par with the Black Mesa Incident. After the rocket launch, Kleiner remains inside to help Magnusson with destroying the Combine Superportal while Alyx, Eli, Dog and Gordon go outside to see the Superportal dissipate.

Half-Life: Alyx[]

Although Kleiner himself does not appear, his book "From Here to There in Under a Second" can be found on the balcony at the start of the game. According to the back cover, it describes the history of teleportation and the potential for its use in the future.

Personality and skills[]

Dr. Isaac Kleiner is a well-mannered, soft-spoken, brilliant and kind man. The doctor has a particular way of speech, constantly using expressions that most other people wouldn't use, such as "Oh, fiddlesticks" or "Oh, fie!". He acts politely towards his allies, mainly towards Gordon Freeman, whom he considers a friend, but also with Barney Calhoun and Alyx Vance, this also includes his irritable co-worker Arne Magnusson. Though having a brilliant mind, his experiments do not always work out, and, despite of him being a scientist, Kleiner is rather distracted, clumsy and forgetful. He would often lock himself out of his office during his employment in Black Mesa; after the Combine invasion, he still seemed to carry on with this trait, forgetting important lab equipment. The doctor is also rather emotional, especially with his Headcrab pet, Lamarr, and excitable, demonstrated by his reaction upon finding out Freeman was alive, and shown as well when his inventions work the way he intended.

Regarding humanity as a whole, he seems to possess great hopes for them, and, in his speech, Kleiner delivers many hopeful and inspiring words for all humans to witness, despite stating in that same hijacked Breencast that he was not a public speaker. However, he also seems to be sympathetic towards the Vortigaunts, as he references them in his speech, considering them valuable allies to humanity and opposers to the Combine. He also carries a deep grudge towards the Combine and their crimes against all of humanity, calling them "malefactors". Throughout Half-Life 2, he helps Gordon, Barney, Eli and Alyx however he can in order to damage and potentially destroy the Combine once and for all, as he hopes to do.

Kleiner is a smart man, author, scientist, once a teacher at MIT and an ally to the Resistance. He is prolific mainly in science, but he is also shown to have knowledge regarding the Xen lifeforms, such as with his pet Headcrab, Lamarr, whom he presumably debeaked, and the Vortigaunts. He also has shotgun that he presumably knows how to use.


D1 trainstation 010004

Old friends reunite.

Gordon Freeman[]

Gordon Freeman was taught by Kleiner at MIT. He then recommended Gordon's position to the administration of Black Mesa, after which they became coworkers. At Black Mesa, Kleiner had apparently a habit of locking himself out of his office and Gordon would race Barney to "break in" to it.[2] Gordon became Kleiner's assistant again as a part of the human Resistance on Earth. He holds Gordon in the highest respects, even though he admits his heroic acts tend to cause trouble.

Barney Calhoun[]

Dr. Kleiner probably knew Barney well through Gordon. Barney would later aid Kleiner in the human Resistance in various ways, though mainly by working undercover in the Civil Protection, keeping the Combine away from his Lab, at no doubt tremendous risk to himself.

Alyx Vance[]

D1 trainstation 05000200

Kleiner and Alyx in Kleiner's Lab.

Dr. Kleiner knew Alyx when she was an infant at Black Mesa, and they were close enough for her to call him "Uncle" in a collage she made. In Half-Life 2 they both work together in his lab, and on sending refugees on foot through the canals.

Eli Vance[]

Eli is almost the polar opposite to Isaac. He is laid back and confident (despite the fact that a Bullsquid took his left leg), whereas Kleiner is reserved, logical, and cautious in most situations. Coincidentally, this is probably why they make such a good team, and their disagreement on the use of Borealis' mysterious contents. They have both known each other and worked together since the days of Black Mesa. Kleiner is also affectionately nicknamed "Izzy" by Eli on various occasions.

Arne Magnusson[]

While Eli is the opposite to Isaac, Arne is simply headstrong with a very short temper. He has no patience for most of Kleiner's input and at times appears to give him many tedious and long tasks.

Behind the scenes[]

Cohrt bust

Bust of "Cohrt", Kleiner's original model.

  • "Kleiner" is a German surname. Related to "Klein", "small" in German, it has several translations, most of the time related to "reduce" or "inferior". "Isaac" is Hebrew, and comes from "Yitzchaq", meaning "he laughs".[3] In the Old Testament, Isaac was the son of Abraham, which God asked to sacrifice to test his faith, though an angel prevented the act at the last moment. As an English Christian name, "Isaac" was occasionally used during the Middle Ages, though it was more common among Jews. It became more widespread after the Protestant Reformation. Kleiner shares his first name with physicist and mathematician Isaac Newton, and the science-fiction writer Isaac Asimov. Perhaps his surname is shared with Albert Einstein's Doctoral Advisor at the University of Zurich, Alfred Kleiner.
  • Kleiner is basically the Half-Life bespectacled scientist model ("scientist01", or "Walter") turned into a real character, as it happened for Walter Bennet. Kleiner's Half-Life 2 appearance was based on Ted Cohrt, an accountant working in the firm about Valve's office. Kleiner's face originally depicted him as much older man,[4][5] but the team changed his mind when they came across Ted Cohrt in an elevator. It is also said that team members sometimes ran into him at Starbucks and the ones who did not know he was Kleiner's face were staring at him, trying to figure out why he looked so familiar.[4]Bill Van Buren, Content Lead at Valve, in Half-Life 2: Raising the Bar After Cohrt was taken as the model, the older Kleiner face was recycled into the elder Counter-Strike: Source hostage. Although the old Kleiner model has nothing to do with Ted Cohrt, it is named "cohrt.mdl",[5] while the final model, based on Ted Cohrt, is simply called "kleiner.mdl". "Walter" is still used as the name of Kleiner's face texture.
  • The current model originally had a green shirt and black tie.[4][5]
Kleiner getting somewhere1

Kleiner in the Episode Two trailer.

  • As suggested by the Half-Life strategy guide, Kleiner's first name was originally "Alex", which was probably changed to avoid confusion with "Alyx".
  • At the end of the Episode Two trailer released August 2006,[6] Kleiner can be seen in an humorous situation in the rocket silo at White Forest, saying "Mmhh... Now, that's interesting! I think we're getting somewhere!", then screaming when sparks spew from the rocket. This sentence/sequence is not featured in Episode Two; the scream is recycled from the scream Kleiner makes when Gordon appears behind him at the end of the teleportation failure at the start of Half-Life 2.


  • At the end of the Half-Life 2 chapter Entanglement, Kleiner is shown poking his head through a door in his lab while holding a shotgun in a possible nod towards the original Half-Life, where a scientist at the end of the chapter Lambda Core is shown holding a shotgun in a similar, scared fashion, and is spawned as the scientist model that Dr. Kleiner is based on.
  • At the end of the Half-Life 2 chapter Entanglement, it can be seen that Kleiner may have used his shotgun against a Manhack, as broken parts of one can be found near his mini-teleport.
  • Kleiner may also be an author, as there is a book with his name underneath the title.
  • Kleiner is very weak, as he only has eight points of health — as such, most hostile characters can kill him in one hit.
  • In Dota 2, another Valve title, Dr. Kleiner is an unlockable announcer.



Half-Life 2[]



Half-Life 2: Episode One[]

Half-Life 2: Episode Two[]

Half-Life: Alyx[]


List of appearances[]


See also[]