Before her death, Gwen Stacy and Norman Osborn had an affair, because Gwen felt sorry for Norman. Gwen became pregnant with twins: Gabriel and Sarah. Norman took the siblings to France where he raised them, claiming to be their uncle. They believed Peter Parker to be their real father, and were furious that he abandoned them and killed their mother. They would train for years to come under Norman's influence for the day that they would meet Peter and kill him for his personal crimes, avenging their mother.
They later meet up with Peter when he visited the grave of Gwen Stacy, where Gabe and his twin sister Sarah attacked Peter in the graveyard, disguised in ninja clothing. But as Peter escaped from them, they then managed to figure out Peter's secret identity as Spider-Man when they saw him manage to stick to a side of a truck that he escaped on.
Later they called Peter on his phone and tricked him into going into a warehouse where they had supposedly held Aunt May hostage. But Spidey only realized it was trick after the warehouse he was in blew up. After that, Gabriel nearly beat Spider-Man to death only to be stopped by his
sister Sarah who told them they should finish him off later and so they left the brutally wounded Spider-Man.
Later on, they meet up with Spider-Man once more on top of a bridge where Gwen Stacy died by the hands of the Green Goblin. Spider-Man tried to convince Gabe and his sister to trust him, trying to tell them the truth of what happened to them. But though his sister believed Spider-Man, Gabriel didn't and he eventually attacked him, trying to strangle him. But the police starting firing at him which stopped him and his sister Sarah got shot in the crossfire and he was kicked into the river below by Spider-Man. Gabriel could only watch as Spider-Man took his sister to the hospital for treatment.
Meanwhile, Gabriel went into the underground lair where Norman had told him to go years earlier. And when he arrived there, that was where he discovered that he was rapidly aging to the point where it would kill him, and where Norman had left his Grey Goblin suit for him. On a video that prerecorded when he came over that he should take another dose of Goblin formula to stabilize him. This ended up making him stronger and even more insane then he was before.
In his new Grey Goblin costume and glider, he came after Spider-man while he was in the hospital and then he dragged outside for a fight, after the two battled back and forth. Sarah came into the scene as well and she shot down Gabriel's glider, and he ended up crashing into the ocean where he washed ashore somewhere else with no memory as to what happened.
The New American Son
Just a day after was taken into custody for his role in Siege, his laboratory (in "his" ) was searched and gutted. The contents of his lab are placed into one moving truck. A hooded man pays the driver in order to obtain the truck and contents, including the American Son armor. The armor can only be worn by someone with Osborn DNA. An unknown wearer has been fighting crime throughout the city. Harry Osborn is running a barely surviving coffee shop, started abusing drugs again and he is being hounded by the tabloids and he is now being suspected of again wearing the American Son armor. What is worse there was a diamond theft and the evidence suggests the wearer of the armor committed the theft. Harry is angry because he is compared to his father and those who have questioned him about the armor (including Spider-Man) find it hard to believe its him. He is angry because his family legacy has him thinking no one thinks he can do good things. Harry is later surprised when he is visited by a stranger, Gabriel Stacy reveals himself as his brother just before he shoots Harry.
He had increased baseline strength, endurance, reflexes, and healing inherited from his father, further enhanced by the use of the Goblin formula (considering this, it is possible that Gabriel is stronger than his father at his prime). He also used the same Halloween-themed gadgets as the other goblins, including: explosive pumpkin bombs, bat-shaped razorblades, and finger-mounted lasers.
Gabriel's a very skilled and well trained martial artist.
Gabriel is also intelligent as his father was and as psychotic and dangerous as him too.
MC-2 Later it was found out that Peter Parker, Spider-Man had a child with Mary Jane and had the exact powers of her father. She then fell under the name of Spider-Girl and Grey Goblin assumed her as his new enemy.