The first time we see Gideon is when Scott and Todd are racing threw Honest Eds and was inside his mind telling him to use his phsycic powers to destroy the store. Then at the end while Scott's band was performing, Gideon was being interviewed for the documentary of Clash at the Demonhead but he only said "no comment" and walked away.
Other times he was seen in blurry images Wallace showed Scott.
Gideon is revealed to be a music producer and night club owner of the chaos theatre. It was also shown that he is currently dating Envy Adams. Later he's shown prepping of the grand opening of the Chaos Theatre for Toronto and Envy Adams solo record. He seems controlling and not caring of everyone else but himself. Later on the grand opening, Gideon sneak attacked Scott but Scott dodged. Gideon then realized that Scott and Ramona weren't dating anymore which made Gideon angry. He then stole the power of love sword, leveling down Scott. He then asked Scott to join the leauge of evil ex's but Scott refused. Gideon then stabbed Scott with the sword killing him. Then Scott came back to life with the extra life he got from Todd Ingram and Ramona joined Scott. Gideon then revealed his plan of putting Ramona in a cryo chamber of Gideon's past girlfriends. Also he revealed he started the Leauge because he got drunk and put a drunken rant on craigslist. He then talked about the glow and how it traps the person inside their mind. Scott and Gideon fought some more and Ramona then decided to use the glow to disappear into subspace but Gideon stabbed her with the sword. Scott then went into Ramona's subspace bag to get inside Ramona's head. Gideon had control over Ramona's head and turned into a giant demon looking monster but turned back into its original form after Scott headbutt Gideon with the glow. Gideon revealed that the glow has no affect on him and cuts Scott diagonaly. Ramona then kicked Gideon out of her head. Back in the real world, Gideon revealed that he has been in both Scott and Ramona's head a lot using the Subspace highway and messed with Scott's memories. Scott gained the power of understanding sword after seeing Gideon snapping at Envy. Ramona also had the power of love sword, so gideon took a sword out of Envy's dress and fought Scott and Ramona. Gideon was defeated and turned into 77,777,777 coins.
Scott Pilgrim Vs. The World (Movie)
In the Scott Pilgrim Vs. The World movie, Gideon Graves is portrayed by Jason Schwartzman.