Gamer

In 2024, inventor and professional computer programmer Ken Castle unveils self-replicating nanites that, by acting like brain cells, allow one person to completely sense the environment and interact with it using another person's body. Castle's first application of this technology, dubbed Nanex, is a game called Society, which allows gamers to control a real person in a pseudo community (much like The Sims or Second Life). This allows players to engage in all manner of debauchery, such as deliberately injuring their "characters" and engaging in rough sex with random people. People who work as "characters" in Society (having nanites in their brain) are very well compensated.
Castle amasses a fortune that surpasses that of Bill Gates virtually over-night, and soon follows up his success with Slayers, a first-person shooter where the "characters" in this game are death-row or life imprisoned inmates, who use real weapons to fight televised battles on specially created arenas. Any inmate who survives 30 matches earns his freedom. The player controls the character's movement, while the character decides when to shoot, and no communication is allowed between the two. The game is known for a lag problem, called the "ping", a small but dangerous delay between the player's command and character's action. John "Kable" Tillman is the crowd's favorite, having survived a record 27 matches, where all others have only managed to survive ten matches at most. He is exclusively controlled by Simon, a seventeen-year-old superstar gamer from a wealthy family.
The technology and the games are not without controversies, and an activist organization called "Humanz" claims that Castle will one day use Nanex to control people against their will. During a talk-show interview, Castle is confronted with questions about a potentially rigged vote which gave Castle control over the U.S prison system and allowed him to operate the Slayers game. In the middle of the broadcast, the network is hacked by the Humanz, which Castle finds amusing. Later, Society is also hacked and gameplay is interrupted, which costs Castle millions, but even then Castle sees it as trivial. However, Castle feels threatened by Kable's pending release, and introduces a new "character" into Slayers named Hackman, who committed several murders and then surrendered in order to be able to participate in Slayers, in the hopes he will get rid of Kable and become the new fan champion of Slayers.
Meanwhile, Kable's wife Angie is working as an "actress" (someone who voluntarily becomes a "character"), and attempts to gain custody of their daughter Delia, but is denied and informed that she has been placed with a wealthy family. Hackman taunts Kable, saying he has no player to control him, and threatens to kill Kable's wife and daughter once he is freed. Kable is warned by a Humanz activist that Castle has no intention of letting him survive his last match, and that escaping is the only option. The activist takes a sample of his blood. Meanwhile, Simon is contacted by the activist, who provides him with illegal mods allowing him to talk to Kable during the game and to relinquish control over his character.
In Kable's 30th game, he convinces Simon to let him control himself, and escapes the arena. News outlets report that Kable has been fragged, which puts Simon in a difficult position: he is labelled a "cheater", locked out of his bank account, and under police investigation for helping Kable escape.
Tillman is found by Humanz activist Trace, the person contacting him in prison. She takes him to the Humanz leader Brother and Dude. They explain to him the danger of Castle's technology, as acceptance of the Nanex technology will eventually grant Castle unlimited power over the populace. Tillman refuses to aide them in their fight against Castle, but Brother informs him of his wife Angie's location as a character in Society.
Tillman goes to rescue Angie and becomes involved in a fire-fight with Hackman and Society's security forces. At the last minute Tillman and Angie are rescued by Gina, a talk-show host/reporter who wishes for Tillman and the Humanz reveal the truth about Castle. They return to the Humanz who deactivate the nanites in Angie's brain as well as Tillman's. It is then revealed that Tillman was part of the original Nanex experiments while in the military, being told it was to replace brain matter with synthetic tissue to improve mental function. Using experimental technology to view Tillman's memories, they learn that in a session designed to test Nanex's capacity for control, Tillman (controlled by Castle) fatally shot his friend and ended up on death row. Tillman volunteered for "Slayers", hoping to earn his freedom.
Upon learning that Castle adopted Delia, Tillman infiltrates his mansion to get her back. He locates Castle, who taunts him and reveals that his henchmen have killed Trace, Brother and Dude. He then controls several inmates to attack Tillman, who kills them all. Castle reveals that he replaced 90% of his own brain with Nanex, but his allows him to control others who are "wired" as long as they are within the range of his control. He plans to release an air-borne version of Nanex which will infect the entire population within six months, giving him ultimate control. Tillman then faces Hackman, now under Castle's control, and easily kills him. However, Castle explains his men have reactivated both his and Angie's Nanex, and savagely beats him while Tillman forced to remain defenseless. Angie and Delia are brought in to witness the scene. Castle tries to force Tillman to kill his own daughter, but he resists the command.
Unbeknownst to Castle, Trace and Gina escaped his henchmen, and broadcasts their confrontation across the country, exposing Castle and his plans. Simon witnesses the broadcast and his control over Tillman is returned. At the last second, Simon forces Tillman to drive his knife into the floor before trying to attack Castle. Castle wrestles for control over Tillman, but Tillman tells Castle to imagine the knife going into his own stomach. Castle unconsciously does so, and it allows Tillman to kill him. Before they leave, Tillman convinces Castle's men to deactivate Nanex, one of them commenting "Well played, Kable".
The film closes with the Tillman family taking a trip down a country road, ending with the words "Game Over".

Question: How much of Castle's brain has been replaced?
Answer: 90%