Isaac Kleiner

Doctor Isaac Kleiner is a fictional character from the video games Half-Life and Half-Life 2. An archetypal 'absent-minded genius scientist', 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 Empire, and a prime member of the Resistance's science team.

He is affectionately referred to simply as "Izzy" by Dr. Eli Vance on various occasions. Some sources also erroneously refer to the character as Dr. Alex Kleiner, based on an apparent inaccuracy in the strategy guide of the original Half-Life.

Half-Life
Although Dr. Kleiner's character design is based on the "bald, glasses" scientist model from the original Half-Life (dubbed "Walter Bennett" by fans and later named as such in the Opposing Force and Blue Shift expansion packs) he is not intended to be the same character, and never interacted with Gordon at all during the Black Mesa Incident. Also, the texture file for Dr. Kleiner's face is called "walter_face.vtf". This is likely to be referring to Walter Bennett. Before Half-Life 2, the only reference in the games to Kleiner was during Half-Life: Decay when Dr. Keller mentions he "[does] not understand what Kleiner sees in that boy," referring to Gordon.

Dr. Kleiner, who recommended Gordon Freeman for employment at Black Mesa, worked with him as part of the facility's Anomalous Materials team and was one of his professors at MIT. He manages to survive the Resonance Cascade disaster of the first game with the aid of Eli Vance, though exactly how he escapes is unknown. One logical explanation is that he, Eli Vance (With his daughter Alyx) and perhaps some other Black Mesa personnel took an SUV and escaped the same way Barney Calhoun, Dr Rosenberg and the other 2 scientists did at the end of Blue Shift.

In the strategy guide for the original Half-Life, a Dr. Alex Kleiner is mentioned, which can be assumed to be the same person. This is likely an error, although it is entirely possible during the development of Half-Life 2 he had his name changed, and is most likely the same person mentioned at the beginning.

Half-Life 2
Along with colleagues (and fellow survivors) Alyx Vance, Dr. Eli Vance, and Barney Calhoun, he makes up the core of the resistance against the Combine. Dr. Kleiner has set up a lab underground in City 17 in an old abandoned Northern Petrol building. 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' and at some points in the game calls 'Hedy' (a reference to 1930s actress and inventor Hedy Lamarr).

A depiction of Kleiner's younger self is also featured in Half-Life 2, appearing on the cover of Popular Scientist, a fictional magazine (and spoof of Popular Science magazine) that would have to be published prior to the Black Mesa Incident. In it, he sported sideburns and had more hair, which is seen as brown in color. 

Half-Life 2: Episode One


In Half-Life 2: Episode One Kleiner returns, appearing on the video screens previously reserved for Dr. Breen's propaganda and instructing survivors to make their way to their nearest train station to evacuate City 17. Kleiner also amusingly informs people that the Combine's "Reproduction Suppressors" are no longer effective, and that "those so inclined" should take advantage of the fact and "do your part for the revival of the species". He also rallies people to prepare for the Combine's retaliation, stating that several new technologies were developed during their occupation, and that these will be deployed as soon as possible to help fight the Combine.

Half-Life 2: Episode Two
Kleiner appears in the third trailer of the upcoming game Half-Life 2: Episode Two. His most relevant scene is at the end of the trailer, in which he seems to be working on some kind of rocket with the aid of Vortigaunts and mentions that they're "getting somewhere". It is believed by many players that this rocket is one of the new technologies that were developed to fight the Combine.