Creation of the League of Evil Exes
Gideon Graves made his fortune by setting up a successful career as a music mogul, at which point he took the alias of "G-Man". Over the course of his career, he met Ramona Flowers at a party in New York and the two quickly formed a relationship, during which time Graves infected Flowers with The Glow. Fed up with him constantly pushing her away, Ramona decided to leave Gideon, leaving nothing except a letter. Unfortunately for Ramona, Gideon walked in on her just as she finished the letter. Ramona, filled with intense emotions, became overwhelmed by The Glow and vanished into Subspace, taking the letter with her. After Ramona left, Gideon got totally wasted out of his mind and put up a huge drunken rant on Craigslist about her. This got the attention of Ramona's other six evil exes who contacted him. Gideon used this opportunity to form the League of Ramona's Evil Exes, which he would use to control the future of Ramona's love life.
Fragmentation of the League
Upon dumping Gideon, Ramona began dating Scott Pilgrim, a member of a band called Sex Bob-omb. In order to continue dating her, he fought and killed Matthew Patel. Shortly afterward, Gideon started spying on Scott and Ramona through Scott's Subspace. Whilst there, Gideon altered some of Scott's memories, adding his likeness to Simon Lee, Kim Pine's ex and "enemy" of Scott's.
In Scott Pilgrim & the Infinite Sadness, Scott took down the third ex, Todd Ingram, during The Clash At Demonhead. He proceeded to take down Roxie Ritcher in a yard after leading Knives' father, bent on killing him, into Ramona's house.
Also in Scott Pilgrim Gets It Together and vs. the Universe, Scott accidentally intruded upon Ramona's head and finds her kneeling beside a sinister dark figure sitting on a throne. Though the shadowy figure's face is never revealed, it can be assumed this was Gideon, or at least a manifestation of him representing the part of Ramona still attached to him.
In Scott Pilgrim's Finest Hour, Scott finally encountered Gideon on the street while he and Envy Adams are talking about their past. Scott is so frightened by Gideon's presence, he immediately runs away.
Later, after confronting his mistakes by merging with NegaScott, Scott goes to the Chaos Theater to confront Gideon once and for all. Gideon ends up stealing the Power of Love from Scott and impaling him with it. Scott returns to life thanks to the 1-Up he gained from defeating Todd Ingram, and he and Ramona begin to fight Gideon. It is then revealed that Gideon is keeping six of his other ex-girlfriends suspended in cryogenic stasis on the ceiling of Chaos Theater, enabling him to thaw and date any one of them at any time of his choosing, and desired to add Ramona to the final capsule.
Using The Glow, Gideon manipulates their emotions, causing them to argue with each other. Ramona tries to leave through Subspace, but Gideon stops her escape by impaling her, and then teleports himself into her mind. Scott then enters Subspace through Ramona's Subspace Suitcase to enter Ramona's mind, where he finds that Gideon has transformed himself into a powerful God form and is lording over Ramona. Scott headbutts him, giving Gideon the Glow and transforms him back to his original size, releasing Ramona from his influence in the process. Infuriated, Gideon tries to kill Scott with his sword, but Ramona enters her own Mind Subspace and casts the three of them back into the real world where she blocks the attack with her Subspace Suitcase, causing it to explode whilst disarming Gideon. Ramona then takes the Power of Love, which heals her wounds allowing her to continue fighting. During this time, Envy asks Gideon if he was all right. Gideon coldly rebuffed her.
After realizing that he and Gideon are more similar than he thought, Scott earns a new sword - the Power of Understanding, and begins the final battle alongside Ramona. Gideon takes his backup sword (installed in the back of Envy's dress) and begins to fight. Gideon reveals during the battle that he was spying on Scott and Ramona through Scott's head via the subspace highway, "spicing up" some of Scott's boring memories along the way. This has further increased the memory problems Scott has throughout the series and prompts Ramona to exclaim "His brain doesn't need any extra damage from you!" Infuriated even more, Ramona disarms Gideon once again, leaving him at the mercy of the duo.
Death of Gideon Graves
Before his final defeat, Gideon claims that getting rid of him won't solve anything and that both Scott and Ramona are their own worst enemies based on their past actions throughout their lives. They soon deny this, however, and reply that Gideon himself is much worse due to his own actions. Having said this, Scott uses the Power of Understanding while Ramona simultaneously uses the Power of Love on Gideon and perform an X-Strike, creating a X-shaped slash mark in his chest. Gideon then explodes into $7,777,777 worth of coins which fell painfully all over the onlookers below.
To be added
Portrayal in adaptions
In vs. the World
In the film adaption, the skirmish is very different and is also much longer.
When Scott infiltrated Chaos Theatre, he encountered Gideon's Hipsters attempting to cut him off from his objective. The first hipster blocked Scott's way and requested a password. Scott replied, "Whatever" - which turned out to be the right answer, and so the Hipster let him through. Two more hipsters, these of whom guarded the elevator, asked Scott for the "second password." Scott gave an exasperated sigh - which turned out to be the correct answer, so they let him in.
Gideon used a Katana hidden in his cane to fight against Scott in the final battle. A slash with this sword from Gideon was able to completely shatter the Power of Love. Gideon then tries to kill Scott, but loses his sword when Knives kicks it out of his hand. While Knives attacks Ramona, Gideon and Scott fight in hand-to-hand combat. Scott eventually throws Gideon off the pyramid steps so he can stop Ramona and Knives' fight. However, while he was trying to explain things to them, Gideon impaled Scott in the back with his katana, and utters the words "Game Over", as Scott fell to the floor, dead. Gideon told his corpse that he could cheat on his exes, but he could not cheat death.
Scott awoke in the desert where his dreams of Ramona had occurred, where Ramona told him she should not be the only thing he was fighting for. Scott proceeded to retry the stage (after revival from the Extra Life he had acquired from the Katayanagi Twins).
Making his way to Chaos Theatre, he re-encountered the Hipsters. This time, he defeated the Lollipop Hipster by telling him: "Your hair looks stupid" causing the obstacle to burst into coins. The elevator guards were taken down with a few well-placed punches.
Scott entered the primary chamber and earned the Power of Self-Respect by declaring that he was fighting for Ramona, but not only for Ramona. He attacked Graves with it, causing him to be knocked down, earning Scott an even 7000 points. After Scott settled things with Ramona and Knives, Gideon regained his feet and impatiently demanded that Scott fight him. He then summons his Pixel Katana and renews the battle. Even though he shattered the Power of Self-Respect, Ramona, who had been able to remove the microchip Graves had planted on her (contradicting the book where Graves planted The Glow on her instead), kneed Graves in the crotch. As he screeched with agony, Knives snagged his sword with her scarf and sent it flying out of his reach. Infuriated, Graves slammed Flowers off the pyramid. He was then overwhelmed by the combined forces of Scott and Knives Chau who use moves from Ninja Ninja Revolution to defeat him.
As Gideon knelt on the floor in defeat, he chided Scott that it took him two hours to get Ramona's exes' contact information in order to form the League, and then tried to once more hope for some last moment cruel demoralization, but instead, Scott booted him in the head, shattering him. Coins showered all over the theatre netting Scott another 7,000,000,000 points. Realizing that Sex Bob-omb's deal with Gideon was over, Stephen Stills hastily began grabbing as much of the reward money as possible, Kim did not join him.
Scott and Knives agreed they made a good team, but then Gideon, who seemingly lived on through his stylish hipster glasses, introduced Scott to Nega Scott before being discarded. Knives and Ramona prepared to fight, but when Scott declared he must fight the new enemy one-on-one, Ramona and Knives went outside. However, both Scott and Nega Scott emerged from Chaos Theatre a few minutes later talking and laughing. When asked what happened, Scott said they just "shot the shit," that Nega Scott was a great guy, that they had "a lot in common" and they were gonna do brunch next week, on Tuesday.