Dr. Nathan Cox is a psychiatrist of a psych ward treating people, especially any veterans suffering PTSD.
Dr. Cox took being a psychiatrist very seriously, helping other people with problems and even veterans who came back from war with PTSD.
Dr. Cox has had a history of helping people in need and in crisis. He's also helped and treated veterans who came back from war who'd end up suffering PTSD. He's been recently treating Chad Jackson, a Navy SEAL veteran, who's currently seeking security guard employment.
Dr. Cox is first seen talking with Riggs and Murtaugh about what all he knows and how long he's been treating Jackson since he's been seeing him and prescribing him the "psychiatry pill" and he told them only little what he could tell hem, but wasn't telling them everything.