John Freeman, who is likely the younger brother of Gordon Freeman, is a man in his early-mid twenties who in the first story of the series, Full-Life Consequences, appears to have a brother complex. He also appears to have a penchant for exaggerated and repetitive descriptions of locations and people and for reaching analogies(ex: "Gordon Freeman is now these hands"). Sometime after the first two Full-Life Consequences episodes, he disappears(unknown means, perhaps stasis like his brother in Half Life?) long enough for the Combine to overthrow Earth's governments and for his son to have grown up almost exclusively in that world.
As aforementioned, John Freeman at first appears to have a brother complex. He idolizes his brother and appears to be somewhat jealous of his adventures, which is why he agrees to join him. He seems to have a blatant disrespect for police officers, shooting one with an unknown presumably ballistics non-weapon after he said he wants to give him a ticket(He was infested and had headcrabs but it appeared that he still had his higher brain functions intact, with his ability to speak). John also seems to be a well-intentioned man with his interactions with zombie "goasts"/ghosts in Ravenholdm. His attempts to be kind are misguided, however, since his solution to the zombie ghosts being zombies in the first place is to destroy their house with an unknown explosive. Despite this, he shows an apparent unfamiliarity with firearms as he fires one the instant he picks it up, and at things he knows very little about.
John frequently shows a commitment to family, particularly his brother Gordon, as everytime he hears Gordan calling out for him he goes faster in his motorbike or on foot, despite risk of arrest or injury. In fact, it seems he would risk his life against "aliens and monsters" he knew nothing about to assist his brother, again despite having no seeming familiarity with firearm combat.
Alternatively, it is a distinct possibility that John Freeman was either not related to Gordan Freeman at all and was imagining an adventure after hearing the name somewhere, or he was Gordan Freeman's brother and grasped at anything, even paranoia and delusional thoughts, to explain his disappearance. This, however, would not explain the events of "Free Man" with any sort of cohesive detail.