Little was known about the past of the first and most successful of the Scourge of the Underworld. From what was known of the organization, he was most likely recruited for the program by Domino and trained by Bloodstain. The first member of the organization to go active, this Scourge was responsible for most (but not all) of the organization's early hits.
The Scourge's first victim was The Enforcer, who had been recently contacted in his hotel room by Madame Masque (acting on behalf of Obadiah Stane). The Enforcer agreed to sprint Stane's agent, the Termite from prison, but was stopped just outside his hotel by a bag lady who asked him for some change. The Enforcer told her to get lost, so she shot him with a sub-machine gun she had hidden in her coat. As the fatally wounded Enforcer fell to the sidewalk, the mysterious assailant proclaimed "Justice is Served!" and disappeared. The declaration would be heard again many times as the Scourge claimed more victims.
Later, the Scourge posed as a passenger on a Bus carrying Miracle Man. When the bus was also boarded by Ben Grimm, he pestered Grimm throughout the ride. Eventually, Miracle Man used his powers to stop the bus, hoping to intercept a prison transport carrying the Rhino and free him. While Grimm and Rhino fought, Scourge revealed himself and shot Miracle Man, again proclaiming "Justice is Served!".
Later, during the Secret Wars II #2, Scourge blasted Psycho-Man's Hate Monger construct after he had already been defeated by the Fantastic Four. She-Hulk attempted to capture the Scourge, but he escaped down an alley.
Disguising himself as an old man, the Scourge later shot Thor's enemy, Megatak. In Another incident at Marvel Comics, a Scourge agent (possibly this Scourge) took advantage of the chaos surrounding a fight between various heroes and the new Lethal Legion to shoot the would-be hero Phone Ranger in the head.
Scourge also attempted to assassinate Constrictor after he was badly beaten by Anaconda because he sold the Serpent Society out to Captain America. Posing as Nurse Emmett, the Scourge convinced a guardian Captain America to leave the room, but failed to kill Constrictor when the Captain returned. Scourge escaped through the window before he could be apprehended. Later, Scourge's plan to eliminate Kraven the Hunter was foiled when Kraven encountered and fought Tigra in central park. The fight drew too many witnesses for him to act, and also made it too difficult for him to get a clear shot without endangering Tigra.
Scourge later killed the Melter's assistant, Keegan, then borrowed his identity to get close enough to eliminate the Melter himself. Soon after, a different Scourge operative (Caprice) disguised herself as Golddigger to shoot fellow Grappler Titania. As she left, she encountered Ben Grimm and Battleaxe, who heard the shot. She blamed the attack on an unknown man, then escaped.
Disguising himself as a construction worker at the Baxter Building, Scourge shot Basilisk out of a window shortly after he escaped his underground entrapment. Disguised as a garbage man, the Scourge shot the Fly. Later, he managed to shoot down a Serpent Saucer piloted by Death Adder, and scored another successful kill when Death Adder "hijacked" a taxi cab, only to be shot when the driver turned out to be the Scourge in disguise. Much later, he posed as a truck driver and assassinated a hitchhiking Blue Streak (SHIELD Super-Agent).
Scourge's finest moment came when Gary Gilbert, formerly Firebrand, assembled several super-villains at the Bar with No Name in Medina County, Ohio to address the growing Scourge problem. The Scourge himself was in attendance, disguised as the bartender, Jake. No sooner had Gilbert called the meeting to order than Scourge attacked, killing all 18 in attendance. The villain killed in the Bar with No Name Incident also included Grappler, Hellrazor, Hijacker, Mind-Wave, Shellshock, Steeplejack, and Vamp. Because the bar had a strict "No Weapons" policy to keep super-powered bar fights from turning lethal, the villains didn't have a chance.
After Captain America learned the extent of Scourge's plan following a battle with Blacklash, the Avengers launched an investigation. The Water Wizard, who had a flat tire on the way to the Bar with No Name and thus inadvertently saved himself, tipped off Captain America about the massacre. Unaware of increased efforts to catch him, Scourge slept in his van until a transmission from Domino awakened him to update him on a number of super-powered villains. Scourge resolved to kill whoever was closest, who turned out to be Diamondback, in the hospital recovering from an injury. Scourge arrived too late, however, and arrived just as Diamondback was broken out by fellow Serpent Society member Cobra.
In order to draw out the Scourge, Captain America posed as a "survivor" of the Bar with No Name Incident, Mirage. The disguised Captain was taken to a cabin in the woods for safe keeping, and was trailed by Domino. When Scourge attempted to assassinate Mirage in his sleep, it turned out only to be a costumed dummy. Captain America gave chase, and caught Scourge after he hesitated to shoot an innocent. Unmasked at last, the Scourge claimed to be the younger brother of the Enforcer, who took up the Scourge identity to clear his family's name. (Since we now know the Enforcer to be Charles Delazny Jr., and an only child, we can assume this to be a lie of the sort often told by unmasked Scourge operatives). Scourge was then shot from a distance by Scourge II to keep him from eventually revealing details about the organization, indicating to everyone for the first time that the Scourge was not a single individual.
The Scourge of the underworld was a master of disguise, and often used latex masks, body padding, and costumes to disguise himself as ordinary people of all ages, races, and walks of life, both male and female. His acting abilities were commensurate with his disguise skills. The Scourge was also a decent marksman. From what was now known about the Scourges as an organization, we can also presume that he was trained by Bloodstain, and thus had some ability in hand-to-hand combat.
Generally the Scourge used relatively ordinary pistols, sub-machine guns, and other arms. One at least one occasion he was shown to use a more sophisticated blaster pistol.