Barney Calhoun, an undecided major after two years at Martinson College, is employed as a mid-level security officer at the Black Mesa Research Facility, with Level 3 security clearance and is accommodated in the Area 8 Topside Dormitories. Presented as a sarcastic, witty, although very capable and adaptable officer. Barney is an upbeat, friendly, charismatic and able man.

Dr. Gordon Freeman is the protagonist of the Half-Life series. Freeman is a theoretical physicist, forced to defend himself and the human race in a conflict against hostile aliens and other enemies after a failed experiment causes a worldwide alien invasion. He doesn't speak, communicating through sign language, gestures, and facial expressions. Possibly gay.

Dr. Isaac Kleiner is a scientist, who 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 leader of the Resistance against the Combine, and a prime member of the Resistance science team. Isaac Kleiner is a well-mannered, soft-spoken, and optimistic man. He has a particular way of speech, constantly using archaic expressions that most other people wouldn't use, such as "Oh, fiddlesticks" or "Oh, fie!". He acts politely and amicably towards his allies, from those he share a friendly relationship with like Gordon and Alyx to more difficult personalities like his co-worker Arne Magnusson. Isaac also maintains an optimistic outlook on things; he generally considers the best outcome even under dire circumstances and often registers bad outcomes in a subdued analytical manner.

As seen on his sweater after hours, Eli is presumably a graduate of Harvard University. Vance is employed at the Black Mesa Research Facility, working in Sector C's Anomalous Materials. As a full-time employee of Black Mesa, he lives in the facility itself with his wife Azian and their young daughter Alyx. Eli is warm, good-humored, and charismatic, holding everyone around him in the aura of his personal charm. He's black. He wears the standard scientist uniform, complete with the itchy tie. He would be that kind of person to call everyone nicknames, like Kleiner, who he calls "Izzy" based on his first name being Issac.