A tablet in the map Argent D'Nur suggests that the Icon of Sin is the reborn and demonized son (or was at least demonized by the Icon of Sin) of the Night Sentinel that betrayed his brethren, unleashed onto his father's realm during the battle that assured hell's victory of Argent D'Nur. As of now, the demon is currently dormant, according to a UAC data log that makes reference to it.