Gideon claims to have awakened in Old Russia, sometime during the Dark Age - although records from that time remain notoriously scarce, it's believed that he's approximately as old as Saladin Forge and some of the other Iron Lords. Perhaps understandably, Gideon avoided the attentions of his fellow Risen in favor of mantling a human settlement in Yenotayevka. He made frequent pilgrimages to the Russian Cosmodrome, and was an early proponent of the threat posed by the SIVA "techno-virus". Though he eventually relocated to the Last City, Gideon remained on difficult terms with the Iron Lords, who famously sought to claim the Cosmodrome for humanity's benefit. Despite his age, however, Gideon was seen as something of an uneducated "bumpkin" by the more experienced Guardians.
Gideon studied under the warlock Nirwin, eventually becoming one of the City's pre-emiment scholars on Golden Age technology, alongside his friend and fellow student Osiris. He supported Osiris in his promotion to Vanguard, but became increasingly uneasy with his friend's obsession with the Vex. In particular, Gideon saw Osiris' insistence on breaching the Vex underworld as analogous to the Iron Lords' suicidal focus on "claiming" the Cosmodrome. Whether or not Osiris was aware of this remains a matter of debate. Though their relationship had become steadily more combative in the lead-up to his expulsion from the City, Osiris seemed somehow surprised that Gideon refused to join him in exile. His proximity to Osiris had managed to destroy his standing in the city, and it would be many centuries before Gideon would find another fireteam. Even then, his position on a group of mostly-young and difficult Guardians was seen as a punishment, rather than a privilege.
Along with the hunter Loveless, Gideon was in the process of infiltrating Gaul's command ship when the Red Legion cut them off from their Light. Having pushed Loveless to safety, Gideon used the last of his Light in a heroic - and ultimately vain - final stand. He spent several months held captive by the Red Legion, being forced to participate in brutal fighting rings. Though he was eventually rescued, the incident left Gideon with what Izzy claims is a form of complex PTSD. The Vanguard have reluctantly allowed Gideon to remain on indefinite shore leave. More recently, Gideon and Izzy helped foil a Vex plot on Mercury, a mission which saw Gideon reunited with Osiris for the first time since his exile.
Gideon's Ghost, Atrox, has always been fascinated by Osiris and Sagira, to the extent that he has the same Ghost shell that she does. Sagira exasperatedly refers to him as a "fanboy". She'd never admit that she enjoys the attention, just as much as Osiris.
Atrox is less stern than his patrician Guardian, although he's just as much of a bookworm. He has a soft, crisp voice, with a peculiarly "upper-class" diction.