The Legion of Super-Heroes first found out about Zaryan the Conqueror when a Science Police Sargeant Esquival asked them for assistance.  Zaryan had robotic raiders attacking an Earthgov manufacturing facility.  After defending the facility, the Legionnaires attacked a ship, thinking that Zaryan was onboard.  The Legionnaires and Sargeant Esquival entered the ship, only to be shot at by the ship's captain, one of Zaryan's raiders.  Esquival jumped in front of the blast, sacrificing her life for Saturn Girl.  Saturn Girl vowed that no one would ever die in her place again. 
 
Later, the Legionnaires confronted another Zaryan raiding ship, hoping he would be aboard.  However, it was just more of his raiders.  Saturn Girl, however was able to figure out where Zaryan's raiders would strike next.  The planet Naltor.  When Zaryan's raiders arrived on Naltor, the Science Police were waiting for them, thanks to the precognitive abilites of the locals, specifically young Nura Nal, the prize student of Beren, the High Seer of Naltor.    
 
During the battle, Nura had a prophetic vision of one of the Legionnaires dying battling Zaryan the Conqueror.  Beren sent a message capsule to Earth, hoping that it would arrive in time to warn the Legion.  Only Saturn Girl received the message, which she quickly destroyed.  She did not want any of the Legionnaires to perish, so she planned on being the only one to face Zaryan. 
 
Saturn Girl rigged the election for Legion leader, assuring that she would be in charge when Zaryan attacked.  Saturn Girl arranged it so each Legionnaire would be suspened from membership when the time came to battle Zaryan.  As Zaryan began his attack, Saturn Girl flew off alone to face him.  However, Lightning Lad sped past her, using his lightning bolts on Zaryan's ship.  Lightning Lad was hit by a blast of cold from one of the ships weapons, and was killed, just as Zaryan's ship exploded. 
 
On an alternate Earth, Zaryan was a Khund warlord, who wanted revenge on Laurel Gand.  It has not been revealed if he is a Khund in the New Earth universe, however.