Dr. Kleiner, who was one of Gordon Freeman's professors at MIT recommended him for employment at Black Mesa by the Civilian Recruitment Division (as the computer voice on the tram mentions) and worked with him as part of the facility's Anomalous Materials team. 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. Along with colleagues (and fellow survivors) Alyx Vance, Dr. Eli Vance, and Barney Calhoun, he makes up the core of the resistance, Lambda (named after the Research Team Isaac, Eli, and Gordan were all working on. It's purpose was teleportation. Other Lambda Scientists can be seen on the photo located on Kleiners lab). 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).

Barney was formerly a security officer at Black Mesa, where his friends included Gordon Freeman and Dr. Isaac Kleiner. Whenever Isaac locked himself out of his own office, Gordon and Barney raced each other through the air duct system in order to retrieve the keys. Barney fought his way out of Black Mesa early during the disaster, and later was lucky enough to meet up with fellow survivors Isaac, Eli and Alyx. Though Barney lacks the scientific expertise of the other Black Mesa escapees, he has a vital role in the resistance working undercover in the Civil Protection police force