Dr. Isaac Kleiner is 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.
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 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.
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, and ultimately did not happen due to the Black Mesa Incident. At this time, Kleiner was also on friendly terms with many co-workers, namely Gordon, Eli and Barney, although Richard Keller stated he did not understand what Kleiner was seeing in Freeman.
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 Norther Petrol building located near the City 17 Trainstation, and began working on teleportation, among other works, while also staying in touch with Eli, who was working in Black Mesa East in the city's outskirts, as well as Mossman, and 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.
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.
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 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.
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.
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 Magnusson 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.
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. 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.
Dr. Kleiner probably knew Barney well through Gordon. Barney would often race Gordon into Dr. Kleiner's office via the air ducts to retrieve Kleiner's keys when he locked himself out. 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.
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 is almost the polar opposite to Isaac. He is laid back and confident, whereas Kleiner is reserved, logical, and cautious in most situations. Coincidentally, this is probably why they make such a good team. 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.
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. Back at Black Mesa, the two competed for grant money.
 Behind the scenes
- Kleiner was first introduced in Gordon Freeman's backstory for Half-Life with the first name "Alex". He was later mentioned in the Half-Life (both PC and PlayStation 2) and Blue Shift manuals, as well as at the start of Decay.
- Kleiner is voiced by Harry S. Robins, the voice of most of the scientists in the original Half-Life and its expansions.
- "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 a Hebrew name, and comes from "Yitzchaq", meaning "he laughs". In the Old Testament, Isaac was the son of Abraham, whom 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 and the late assassinated Israeli Prime Minister Yitzhak Rabin.
- 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, 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. After Cohrt was taken as the model, the older Kleiner face was recycled into the elder Counter-Strike: Source hostage (#4). Although the old Kleiner model has nothing to do with Ted Cohrt, it is named "cohrt.mdl", 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.
- At the end of the Episode Two trailer released August 2006, 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 nod towards the original Half-Life. 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.
- Kleiner appears in Dota 2 as an official announcement pack. When enabled, this pack replaces most of the lines in Dota 2.
- Kleiner is Marc Laidlaw's favorite character in Half-Life 2.
 Half-Life and expansions
 Half-Life 2
 Half-Life 2: Episode One
 Half-Life 2: Episode Two
Kleiner holding Alyx's EMP Tool at White Forest.
 List of appearances
- Half-Life instruction manual (First appearance)
- Half-Life: Blue Shift instruction manual
- Half-Life PlayStation 2 instruction manual
- Half-Life: Decay (Mentioned only)
- Half-Life 2
- Half-Life 2: Raising the Bar
- Half-Life 2: Deathmatch (Book only) (Non-canonical appearance)
- Half-Life 2: Episode One (Video only)
- Source Particle Benchmark (Game files only) (Non-canonical appearance)
- Half-Life 2: Episode Two
 See also
- ↑ The Raising the Bar identifies the man in the image as Eli Vance. This is a mistake. The design of the character matches the description of Kleiner from Marc Laidlaw's short story, "Old Friends". In this story, Kleiner is described as a man who wore an eyepatch over his left eye, and that side of his face was a mass of twisted scar tissue.
- ↑ 1.0 1.1 1.2 Half-Life 2 Prima Guide
- ↑ 2.0 2.1 2.2 Half-Life 2
- ↑ Half-Life 2: Episode Two
- ↑ Half-Life: Blue Shift
- ↑ 5.0 5.1 Half-Life PlayStation 2 instruction manual
- ↑ Half-Life: Decay
- ↑ 7.0 7.1 7.2 Half-Life 2: Raising the Bar
- ↑ Half-Life 2: Episode One
- ↑ The Half-Life Story on Planet Half-Life (archived)
- ↑ Behind the Name - Isaac
- ↑ 11.0 11.1 Playable Half-Life 2 leak files
- ↑ Half-Life 2: Episode Two Trailer on Combine OverWiki's YouTube channel
- ↑ Marc Laidlaw's tweet (July 7, 2013 - 11:08 PM)
- ↑ Half-Life 2: Raising the Bar (uncorrected proof), page 360