Paul Johnstone grew up as a troubled youth in Leek, Staffordshire. He avoided a life of crime due in part to the encouragement of a man named Richard Woodroe, who was originally assigned as a caseworker to Paul when he was caught stealing, and eventually married his mother, becoming his stepfather.
Eventually Paul became a lawyer and, beyond that, a district attorney. While his life was going so well, his half brother Hojo had taken his success in college, moved to Wall Street and developed a coke and crack addiction. Using Hojo, some gangsters tried to leverage Paul into letting their men off, but Paul refused. Soon after he ended up the target of an assault intended to serve as an example to others who got in the way of these mobsters. This incident culminated in his attackers injecting him with HIV-infected blood.
After the encounter, Johnstone was left uncertain regarding whether he had been infected or not. The attack had been made public and word of his possible infection spread through Johnstone's workplace, making it a very inhospitable environment to be in. Tensions between Johnstone and one of his co-workers led to an altercation between the two which landed Johnstone out of a job and in jail.
After he was released, Paul received medical confirmation that he was HIV positive and he descended into depression. While walking the streets to clear his head, Paul was threatened by a group of young gang members. He went berserk and attacked them, leading to his brutal mugging and return to the hospital. During this time he resolved that he would use the rest of his time to dispense justice to the individuals who preyed on innocent victims. One of his friends, a cop named Christina Reid (who had been kicked off the force that day for use of excessive force), was also in the hospital and came to visit him. She informed Paul that she and a man named Carlton Sun had been developing an exo-skeleton suit of armor that could help aid him in accomplishing this task.
Johnstone decided to don the suit, christening himself "ShadowHawk" after his favorite superhero (a name that would eventually lure out the psychotic and racist villain Hawk's Shadow, who believed he was the one entitled to bear the mantle of ShadowHawk), and was taught how to fight effectively with the help of Christine, promising to "take back the night." Johnstone also kept the pills needed to slow his reaction to his HIV infection in small pouches on his belt so he could take them as needed.
Early on, ShadowHawk's actions against criminals were brutal. He would catch violent criminals in the act and break their spines, leaving them to be discovered by police with no indication that he had attacked them other than hearsay from the criminals. This led to ShadowHawk garnering a reputation as an urban legend as well as being hunted by both criminals and law enforcement alike.
Later in his career (and as his lifespan shortened due to the progression of HIV to full blown AIDS), Johnstone eventually grew to be less violent. He would also spend a majority of his remaining time searching either for a cure to his infection or another way to extend his life. This led to encounters with the likes of Supreme (in which a battle would ensue, leading to the discovery of ShadowHawk's true identity to the world), the WildC.A.T.s. (who offered a possible solution involving a robotic body to transplant Johnstone's consciousness into - which would ultimately fail to work)  and Youngblood's Chapel (another hero also infected with HIV). One of his few regrets was that he never got to join a super-group, as in his search for a cure, he had realized how useful and fun fighting in a group was.In his final act as ShadowHawk, Johnstone would rescue his mother from being attacked by Hawk's Shadow. The aftermath of the fight would leave Johnstone in a weakened state and unable to elude the pursuit of the police. He was remanded into custody and transported to a hospital where AIDS eventually took its toll and ended his life