Gwen Stacy is a classmate of Peter Parker, and daughter of NYD Police Captain George Stacy.
Gwen once stopped high school bully Flash Thompson from beating up Peter just because he wouldn't take a picture of Gordon getting bullied. Later, after various flirtatious encounters, Peter asked Gwen out, and eventually revealed to her his true identity as Spider-Man, mainly because, at the time, he thought she was the only friend he had.
When the Lizard planned to use reptilian DNA to turn the entirety of New York into humanoid lizards, Gwen helped Peter stop his plan by firstly, clearing out Oscorp when Lizard was on his way to get the serum he had made, and then making a cure for the serum. Gwen hid in a small vent to prepare for the Lizard's arrival. When the beast arrived, it sensed Gwen's presence and started searching for her. After finding her, Gwen jumped and, out of reaction, pulled out a small blowtorch and fired at the Lizard. He left, leaving Gwen unharmed, having already retrieved what he needed and left.
Soon, the Lizard took the life of Gwen's father, Captain George Stacy, whose dying wish to Peter was that the two remain apart for her own protection. Gwen later confronted Peter about her father's wish for them to be apart, but Peter was unresponsive to everything she had to say. Despite this, Peter still chose to talk to Gwen claiming the best promises are the ones that are the hardest to keep.
Spoilers from Amazing Spider-Man 2
Gwen continues to work at Oscorp, under control of Harry Osborn, Peter's best friend, but because Peter keeps breaking his promise to Gwen's father to stay away from her he continually breaks up and makes up with her so to settle they try being just friends. Their relationship is further strained when Gwen tells Peter that she is moving to Oxford University in England. Gwen witnesses Peter, as Spider-Man, his first fight with Max Dillon aka Electro who is also an employee of Oscorp and when she begins looking into Max's incident, she is shut out and forced to run from the company. Later when Gwen is in a taxi for the airport, Spider-Man leaves a message in web on the bridge saying "I love you" and he then swoops her up onto the bridge and tells her that he is going to Englad with her. However their reunion is cut short when Electro starts shorting out the power to the city and Spider-Man and Gwen work together to stop Electro first by making Peter's web shooters electric-proof with a car battery and then by reversing the electrical charge so Spider-Man can fire it at Max and kills him. But when the struggle is over Harry, now the Green Goblin, flies in and deduces Spider-Man's identity as Peter, becomes enraged and kidnaps Gwen and drops her from a building. However Peter is able to intercept her but Harry follows and fights Peter and Gwen is left dangling in the tower and during the struggle she falls but when Peter tries to grab her with a web, she hits the ground as it grabs her. Gwen's death sends Peter into depression for 5 months, but finally after a talk from Aunt May and watching Gwen's graduation speech he is able to resume being Spider-Man in honor of Gwen's memory.
