The G-Man, or simply G-Man, is a key, yet mysterious and enigmatic character in the Half-Life Series. He is known to display peculiar behavior and capabilities beyond that of a human and his identity and motives remain almost completely unexplained.
Physically, the G-Man appears to be a middle-aged Caucasian male with a tall, thin physique, pale skin, a prominent widow's peak, black hair shaped in a military-style crew cut, and pale green eyes. At first he would appear to be some kind of manager, or government figure; this is emphasized by the fact that he is professionally dressed with a blue suit and is always carrying a briefcase.
The G-Man is one of the first characters the player come across in Black Mesa, first seen as his tram pulls into Sector C shortly before Gordon Freeman's arrival at Black Mesa. He appears periodically as he observes Gordon on his adventures through the facility.
G-Man speaks in a slow, raspy yet commanding manner, with a certain accentuated low-key moroseness to his tone, bordering on the cryptic. He also has an odd habit of placing unusual stress on syllables, stressing the wrong parts of words, making unneeded pauses and awkwardly changing the pitch of his voice. He also has a tendency to elongate consonants, especially the "S". Also the G-Man possesses an almost disinterested demeanor, particularly apparent in the ruined and alien-infested Black Mesa Facility (he can often be seen calmly straightening his tie, regardless of whatever chaos may be going on around him). He also has a bit of a dry sense of humor.
The G-Man is often seen in places the player can't currently reach. And once the player does arrive in the area it isn't always clear how the G-man managed to reach it first, or indeed how he managed to leave them prior to the player's arrival. And if he is fired upon, the player's bullets simply doesn’t cause any harm and he never reacts to the shot. Also he is able to teleport the player to and from areas, as shown in the final chapter of the game, where the player appears to be moving at great speed through space on the Black Mesa tram. This suggests the G-man may possess abilities which could be considered non-human.
Participation In The Plot
The G-Man is first seen along the Sector C Line, standing in an electric tram frozen on the track opposite the tram that Freeman is traveling on during Inbound, but he somehow manages to arrive at the Test Labs before Freeman. Prior the experiment with the Test Sample, the G-Man can be seen arguing heatedly with a scientist in a locked, sound-proof room of the Research section of the Anomalous Materials Lab where only mumbling can be heard. Following the catastrophic Resonance Cascade which commences the game's action through Black Mesa, the G-Man can be seen quietly observing Gordon Freeman in several out-of-reach areas as the game progresses.
After Gordon defeats the final boss, Nihilanth, the ruler of Xen, G-Man brings the player to "safety" in an inexplicable, abstract sequence, appearing beside Gordon, having stripped him of his weapons, claiming that "most of them were government property" as being his excuse for having taken them from Gordon and showing him various areas of Xen. The G-Man tells Gordon that he has been observing him very carefully and praises him on his actions in Xen, which is now in his "employers'" control. As he says this, dead HECU Marines, destroyed tanks and a downed jet fighter can be seen around this area of Xen, suggesting that U.S. military forces participated in capturing Xen for the G-Man's "employers", although this may merely be part of G-Man's illusions. Eventually the scene changes into what appears to be a Black Mesa tram traveling through space at high speed. The G-Man then informs that he has recommended Gordon's services to his "employers", and offers him a job. Then, to the player is given a Hobson's choice, the "illusion of free choice": declining the offer results in the unarmed Freeman facing a horde of hostile alien grunts as the screen fades to black with the G-Man's final words; "No regrets, Mr. Freeman."
The choices he offers the player suggests he possesses great power, although his final speech in Black Mesa also suggests he is working for someone even more powerful who may be preparing for something larger than the events at Black Mesa.
Although very little is known about the character, there are many theories as to who or what the G-man is, or indeed who he is working for, but the Half-Life series does very little to answer these theories.
The G-Man Sightings
The G-Man is notable for appearing several times, often in out-of-the-way locations. It may be difficult for a first-time player to see him, and it is almost universally impossible to go directly to where he is standing. When it is possible, he walks away and vanish without a trace from that place before the player is able to reach it.
This list includes all the in-game locations where G-Man is seen, excepting the ending sequence in which he speaks to Gordon Freeman directly.
- Black Mesa Inbound (bm_c0a0c): During the tram ride, he can be seen standing with a scientist in another tram frozen on the track, just before the passage above the loader near the radioactive water leakage.
- Anomalous Materials (bm_c1a0a): The G-Man can be seen standing in an inaccessible room arguing with a scientist, where only a mumbling can be heard. After a short period looking at the room, both G-Man and the scientist will look back at Freeman after noticing his presence, and the scientist will close the window blinds.
- Unforeseen Consequences (bm_c1a1c): After the Resonance Cascade, he can be seen watching Gordon from a catwalk. When Gordon arrives at the same spot, it is revealed that the G-Man disappeared in an apparent dead end, where a zombie is eating a dead scientist.
- Office Complex (bm_c1a2c): Near the broken elevator shaft, the G-Man can be seen behind a locked door in a dark corridor with malfunctioning lights, watching. As usual, he straightens his tie and walks off along that corridor until disappear in the darkness.
- We've Got Hostiles (bm_c1a3a): Immediately before Gordon's first encounter with the HECU Marines, the G-Man is seen on a high catwalk, apparently heading towards the soldiers. However, when Gordon arrives at the same spot, the Marines have only just arrived, whilst a nearby scientist does not mention having seen him.
- Power Up (bm_c2a1a): When Gordon arrives at Sector E Track Control, he sees the G-Man watching him from a control room moments before the Gargantua’s arrival to fight the Marines. By the time Gordon gets in that control room, though, the wounded security guard there indicates no sign of having seen him.
- Apprehension (bm_c2a3b): In a large room filled with three giant industrial pistons, the G-Man can be seen in a catwalk at the far end of the place. He leaves in a direction which leads to a server room with several headcrabs and vortigaunts.
- Questionable Ethics (bm_c2a4e): In the deserted Biodome Complex, The G-Man watches Gordon through a window, standing on a raised floor of a room filled with headcrabs and cirurgical instruments.
- Lambda Core (bm_c3a2g): In this chapter it is learned that the G-Man is able to “think with portals” and suddenly disappear by using them: Gordon watches through a window into a deserted room the G-Man stepping into a glowing yellow portal and vanish from the place right after.
- In the Anomalous Materials sighting, the words of the mumbling chat between the G-Man and the scientist will still be impossible to hear even when noclipping inside the room. If the captions are enabled, the looping sounds of chat will be descripted by many looping and different adjectives: "indecipherable mumbling", "incoherent murmuring", "imperceptible garbling", "inaudible muttering", "inscrutable utterances", "inexplicable prattling" and "incomprehensible droning".
- If the player shoots G-Man directly, he will not die or react to the shot, but he will show blood stains in his body when shot with the crossbow.
The G-Man model used in Black Mesa is the same used in Half-Life 2: Episode 2, but re-skinned to a darker version to stay true to the original. 
The character is voiced in Black Mesa by Kevin Sisk.
The G-Man, as seen in the Official Trailer.
Comparison to Half-Life
- The G-Man doesn't brush the suit lapels with his hands as often happens in Half-Life. He only straightens his tie.
- The character model doesn't have a Black Mesa labeled briefcase, neither its hidden contents.
- The sighting in Black Mesa's Inbound is more subtle than the Half-Life's, because this time the tram doesn't stop near the G-Man's tram like in the original ride.
- The eighth sighting (Questionable Ethics) is non-existent in Half-Life.