Guilty Guilty is a psychopath, to say the least. He kills people without a second thought, and leaves you to die if you dont help him. He has a little gang of buddies, notably 2401 Penitent Tangent and 049 Abject Testament, and they are all cheerfully hateful of everything. Especially the Gravemind.
He was assigned to caretake for Installation 04, but he's not happy when people release the parasite stupidly contained there. After Humans landed on his ring and he realised that he could destroy the Flood on the ring, but in the process destroy all life in the Galaxy, he opted to simply trick someone else into doing it for him, and that someone was Johnny. After leading Johnny through a nightmarish maze of monochrome walls and elevators, He finally gave him the Index and told him to activate the ring. Cortana stopped him at the last minute, however, and thus started Guilty's eternal hatred of having constructs in his core.
Guilty survived the destruction of his ring despite chasing Johnny for hours and turning off the self destruct. After the Battle of Installation 04 he flew all the way to the Threshold Gas Mine and taught a gang of Covenant some fashion sense, thereby creating the Heretic Faction. After these were destroyed by the Arbiter during the Threshold Gas Mine Incident, Guilty Guilty fell into possession of the Covenant, and he told them about the so-called 'Sacred Icon', actually the Activation Index for Installation 05. After being brought to the ring by Tartarus, Guilty helped protect Miranda Keyes from him and divulged the truth about the Halo Array to him in an attempt to calm him down. This failed, and the Arbiter was forced to burn him alive with a Beam Rifle and then teabag his corpse. Guilty then told the heroes about the Ark.
After travelling with the Covenant Separatists for a while, Guilty arrived at Flood-controlled Voi and entered the gutted hull of the Doubt and Treachery, where he found his old pal Johnny. The two made amends and took a message from Cortana to the Shadow of Intent, where Guilty attempted to fix the damaged storage device on which it was kept. After this, he followed the Arbiter around and played peek-a-boo with some Marines, who were not happy that the Arbiter took all their Flamethrowers.
Guilty Guilty followed the Human-Elite alliance to the Ark and helped decode the Cartographer there. Afterwards, he realised that there was another Halo being built there, none other than a duplicate of his own ring. Overjoyed, he told his new friends that it would be ready in just a few days, but for some reason they wanted to activate the ring now, before it was ready. They claimed that it was because of the impending doom presented in the form of the Gravemind, but that couldn't be true, could it?
Nevertheless, Guilty killed Invincible Johnson and attempted to kill Johnny, only to be blasted into smithereens in the process. His beloved Ring soon met a similar fate. His legacy was that he was an annoying flying blue light bulb with a tinny voice and a psychotic disposition.