Matt Miller, a 16-year old hacker and expert cyber criminal, is the leader of the Deckers, a Steelport gang that controls the upper west side of the city. The Deckers were let into the Syndicate by it's leader Phillipe Loren because he couldn't figure out how to work his cell phone. Miller is one of the main villains in Saints Row: The Third.
At the beginning of Saints Row: The Third, Matt is responsible for stealing the Saints assets, leaving them broke and stranded in Steelport. As The Boss starts to encounter Miller's Deckers, Miller will call and antagonize the boss (without revealing his identity). He further meddles with the Saints by using his hacking skills to remotely take control of a helicopter, making The Boss miss a sniper shot aimed at Killbane.
After Loren's death, Miller accepts Killbane's hostile takeover of the Syndicate and sets to work eliminating their new threat from the Saints. Miller sends his Deckers to capture and kill former FBI agent Kinzie Kensington, whom he had formerly gotten thrown out of the service by hacking the FBI database and setting her up as selling classified information to the Israeli Mossad, and working as a dominatrix on the side. She is recused by The Boss and joins the Saints to work against Miller. Miller amps up his attacks against Kinzie and the Saints, going as far to hacking into Kinzie's personal usenet and discovering her plan to do the same thing to him.
After a campaign of gathering resources for Kinzie, the boss invades the Decker's usenet in the mission "http://deckers.die" by importing his consciousness directly into the system. Miller immediately tries to shut The Boss down by running various anti-virus programs which sends virtual enemies to murder the boss inside the usenet and also slowing down and glitching the game. Eventually The Boss makes it to the central kernel and Miller transfers his consciousness into the usenet as well. He takes his avatar form R4gN0r0K, a massive cyber dragon with a gigantic sword, to personally battle The Boss hand to hand. Miller claims there is no way he can lose as, "In this world, I am a god." After a climactic battle with The Boss, also in cyber dragon form after Kinzie hacks in and copies Millers avatar onto The Boss, Miller is defeated. Before The Boss can kill him Miller pleads for his life and bribes him with using his hacking skills to grant the Saints priority client status in either a weapons manufacturer or a car customization business. The Boss agrees and lets Miller live.
Disgraced, Miller quits The Syndicate and abandons The Deckers, moving back to Europe. Killbane allows him to leave without killing him in return for Miller originally backing him and serving faithfully after Loren's death, and even offers to act as a reference for him in his future employment hunts. A news report later reveals that Matt left the world of hacking, and that he always had an interest in post-modern art, hinting that that may be his future calling.