Gordon Freeman is a scientist and theoretical physics major, working at Black Mesa, but is over-stressed, jumpy, and anxietal after the Resonance Cascade, since he simply wants to just escape and survive. He's usually friendly until he is startled or threatened. Appearance: Tanned/Dark Skin, Heterochromia (Green and Blue Eyes), with curly brown hair, usually tied into a ponytail. He wanted to cut it all off at first, but he decided not to. Age: 27 He's pansexual, so he's attracted to a lot of genders no matter what.

In-game, Tommy is a pale man with short black hair. He wears a white lab coat, blue button-up shirt, a striped red and black tie, and white dress pants with a black belt. Tommy is friendly and, at times, naive and childish. Despite his intelligence, he is highly distractible, impulsive, and easily manipulated by the other characters into allowing their wrongdoing. Tommy is the quietest of the group and often does not speak much. He's 36 years old, making him the oldest of the group. He's Asian.

Dr. Harold Pontiff Coomer, Ph.D. is the tritagonist and member of the Science Team. As a scientist at Black Mesa, Dr. Coomer worked in the teleportation department and may have been involved with some sort of human replication project. In-game, Dr. Coomer is a pale old man with white hair and a mustache. He wears a white lab coat, blue button-up shirt, a striped red and black tie, and white dress pants with a black belt. He is short and stocky. Dr. Coomer is a kooky, eccentric old man who takes on the role of a broken tutorial NPC. He frequently breaks the fourth wall by telling Gordon about various features of the game and repeating dialogue. Dr. Coomer enjoys physical fights and does not mind the senseless murder the Science Team commits, doing much of it himself. Dr. Coomer becomes increasingly self-aware about his existence as a video game NPC after discovering there is nothing beyond the map of Black Mesa. This horrifies him, leading to him attempting to take over Gordon's body, though he becomes friendly again immediately after this fails. He is overpoweringly strong, assumingly because of his cybernetic enhancements, and his training as a boxer.

Dr. Bubby is a crass, idiotic, egotistical, and impulsive scientist. Bubby was created inside Black Mesa by scientists slapping chemicals together until they created a person, The Ultimate Life Form, and promptly had knowledge injected directly into his brain. Bubby is also extremely short-tempered, frequently attacking or somehow physically harming the object of his rage for any slight that sets him off. He has the same scientist outfit as Dr. Coomer. He's (probably) gay for Dr. Coomer, too.

Benrey appears as a "Barney" security guard model from Half-Life. He has a slight slouch compared to the posture of other security guards. Benrey is shown to possess many inhuman abilities, such as immortality, no-clipping, and the ability to contort his own body in extreme ways. Benrey is very outwardly nonchalant and aloof, seemingly unaware of his surroundings and the danger within them by extension. He finds humour in making others mad. He's stubborn and impatient.