Nothing is known of the origins or history of being identifying itself as Xnon.  While appearing in essentially humanoid form, it is not known whether this is his true form or an artifice created to interact with Earthly beings.  The first known encounter with Xnon occurred in October of 1940 when a highly modern locomotive, the Black Chief Limited, was carrying a historically large gold shipment from Fort Knox into Cliffland, New Jersey. As the train passed an intervening station, it suddenly vanished into the ether, leaving only an image of the Spectre standing over the spot from which it vanished.  Officers witnessing the event declared the Spectre the culprit, making news the next morning when Jim Corrigan was reading the morning paper.  Knowing he - the Spectre - had not been near there, he left to investigate. 

En route, he stopped to thwart the robbery of a jewelry store and as the perpetrators fled, they do vanished into the ether.  Giving chase into the void, he saw the criminal's car approach and disappear into a large globe.  Rendering himself invisible, his pursuit led him to see the criminals sharing their loot with an armored figure they named Xnon.  He also witnessed the men from the Black Chief Limited being abused by a slave master, whom he quietly disarmed.  Despite his visibility, Xnon called him by name and commanded him to appear, which the Spectre felt compelled to do.  Using a Power Rod powered by "Black Science", Xnon assumed control of the Spectre, demanding he return to Earth and murder the entire Cliffland Police Force.  Unable to resist, the Spectre fled back toward Earth.

Once there, he created mayhem but resisted mightily the urged to killed the officers.  Before he could be fully compelled, he is summoned into the presence of God.  He beseeches the Almighty to help him fend off the influence of Xnon.  In response, a ring appears on his finger, The Voice shares that this Ring of Life cannot be defeated by science or magic and the Spectre feels the influence of Xnon release.  Speeding back to the Xnon's Globe, he quickly dispatches the train and kidnapped men back to Earth and returns to reveal himself to the would be conqueror.   Xnon is shocked when the Power Rod has no effect on the Spectre and more shocked when the Ghostly Guardian destroys his globe and everything within in it.  The two then grapple out in open space until a passing meteor catches the Spectre's eye.  Using all the forces at his command, he captures Xnon with the meteor and sends it hurdling into space (More Fun Comics #60).

Whether Xnon ever returned has not been documented.