Issac Kleiner

Dr. Isaac Kleiner is a Caucasian American 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.

History
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.

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.[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.

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.