Matrix was a Jedi apparently named after "a really annoying math concept." He rescued Fabio, AKA Izzy, a reincarnation of Isildur, from random shadow tentacle thingies, and intended to recruit him to fight "a great evil" (which involved gratuitous evil twins).
After returning Isildur to Middle-earth, Jay and Acacia stole Matrix's lightsaber. While Matrix was busy having an insanely long flashback, the agents killed off evil twin Darth Matrix and his sidekick, Darth Rekka. Then they ambushed Matrix at the door to Fabio's apartment and killed him with his own lightsaber.
The body was left to disappear along with the uncanonical setting of the fic.