Norman Osborn fathered twins, a boy named Gabriel and a girl named Sarah, with Gwen Stacy to whom she gave birth while in France. Gwen vowed she would raise them with Peter Parker and refused to allow Norman access to them. Seeing her as a threat to his potential heirs, Norman killed Gwen as the Green Goblin and then raised the two children as their 'uncle'. Due to Norman's enhanced blood, the twins aged about 2-3 times faster than normal and became adults within the span of a few years. Norman lied to them saying that Peter was really their father and was responsible for their mother's death.
Once they were old enough, the twins set out to kill Spider-Man. Peter Parker received an unsent letter written years ago by Gwen Stacy. He could tell that there were faint traces of writing on the other side, so he had tests performed on it by a forensics lab. The tests revealed text stating that Gwen had been pregnant and had twins. He collected DNA from Gwen's grave and proved that the twins, Sarah and Gabriel were her children. Mary Jane Watson then revealed that she had known for years that the twin's father was Norman Osborn.
Attempting to set them straight (and stop their assassination attempts), Spider-Man met Sarah and Gabriel at the place of their mother's death on the Brooklyn Bridge, to tell them that their father had been manipulating them. Sarah began to believe Spider-Man, but Gabriel remained convinced that Spider-Man was their father, and became outraged that Spider-Man had abandoned them and was attempting to pawn them off on Norman. Gabriel attacked, but Spider-Man refused to fight back, not wanting to hurt him. Police became involved, shooting at them and wounding Sarah. Gabriel escaped and found a base Norman had told them about. There, he discovered that Peter had been telling the truth and injected himself with the Goblin Formula and donned a gray version of the Green Goblin costume, becoming the "Gray Goblin" in an attempt to gain the strength to finally kill Spider-Man.
Attacking at the hospital where Spider-Man was saving Sarah's life, the Grey Goblin was ready to kill Spider-Man in his weakened state when his twin sister intervened, shooting at her twin brother, causing the Goblin Glider to blow up as well as Gabriel to contract amnesia.
Sarah secretly took him home to Paris where she cared for him. Unfortunately, a drug dealer from their youth came after the both of them for the theft of $1.5 million dollars of drugs Gabriel stole from him. The pressure became too great caring for him and fending off the dealer, and Sarah attempted suicide. While she was in the hospital, he escaped the Osborn estate in a crazed state, and Sarah eventually joined Interpol in an effort to find Gabriel.
Years later, Gabriel Stacy resurfaced and shot his half-brother Harry Osborn in a fit of jealousy over Norman's spoils. Leaving him for dead, Gabriel stole the American Son Armor and fled. Continuing to suffer from the split personality disorder he'd developed as a result of injecting himself with a second dose of the Goblin Serum, Gabriel now committed crimes as himself while his 'American Son' persona undid the damage. The American son persona identified itself as the part of Gabriel that recognized that what he was doing was wrong. Recovering from the injury, Harry was informed by his father that Gabriel was, in fact, his brother.
Gabriel's escapades as both his criminal self and his American Son alter ego continued, often being thwarted by Spider-Man. After kidnapping reporter Norah Winters, Gabriel made another attempt on Harry's life, luring Harry to a vacant warehouse. Harry began to fight Gabriel while attempting to convince him that their father was nothing but evil. Gabriel ignored him and continued to fight his brother, only for Harry to deactivate the American Son armor via remote. Essentially powerless, Gabriel and Harry became trapped in the ensuing fire resulting from the fight, until they were saved by Spider-Man.
Gabriel was taken to a psychiatric hospital to receive treatment for his split personality disorder and criminal past. While there, he received a package containing the American Son helmet and a note from Norman saying that Norman loved and missed him.
Powers and Abilities
Gabriel was born with inherited abilities from his father Norman, including super strength, reflexes, healing, and endurance as well as accelerated aging. He later injected himself with a 'second dose' of the Goblin Formula, and thus increased his existing abilities as well as attained new ones:
Superhuman Strength: His inheritance combined with the super soldier serum & the Goblin Formula have fortified Gabriel's musculature, connective tissue, and bone structure, granting him superhuman strength that is much greater than his father's own physical strength. He possesses sufficient strength to lift in the 800 lbs-25 ton range.
Superhuman Stamina: His inheritance combined with the super soldier serum & the Goblin Formula have increased the overall efficiency of Gabriel's musculature. As a result, his muscles produce less fatigue toxins during physical activity than the muscles of normal humans.
Superhuman Reflexes: Gabriel's reflexes are similarly enhanced by his inheritance combined with the super soldier serum & the Goblin Formula, and are superior to those of the finest peak-human specimen.
Regenerative Healing Factor: Gabriel's inheritance combined with the super soldier serum & the Goblin Formula has increased his natural healing abilities & allows him to heal damaged tissue much faster and more extensively than even his grandfather is far from capable of. This healing factor has healed his genetic damages, thereby destroying his rapid aging & might have granted him an ageless immortality. His strong healing factor might make him potentially immortal.
Fighting Skills: Gabriel has had great training in hand to hand combat, marksmanship & strategic / tactical planning.
High Endurance: His amazing constitution allows him to mentally block out pain done from extensive physical damages & allows him to still continue fighting. This naturally developed endurance has made him far tougher and more resistant to injury than the finest peak-human specimen.
Rapid Aging Factor: Before taking the Goblin Formula, Gabriel aged at a much faster rate than humans (physically aging about 2–3 years in one year chronologically.) Had he not taken the Goblin Formula this would have presumably killed him.
Split Personality Disorder: Gabriel began suffering from split personality disorder upon receiving his 'second dose' of Goblin Formula. Norman warned him this was a possibility. It causes Gabriel to perform conflicting actions and continues to plague him as American Son.
American Son Armor
Goblin Weaponry: Gabriel uses the same Halloween-themed gadgets as the previous goblins, including;
Explosive Pumpkin Bombs
Grey Goblin in Spider-Man Unlimited
Grey Goblin about to crash through a window
Spider-Man beating the Grey Goblin in Spider-Man Unlimited
Gabriel is very much insane, possibly even more so than Norman Osborn.
Gabriel's last name was never officially revealed. It is possible that it is his mother's, his biological father's, or his alleged father's, but it is assumed to be his mother's.