Xen was created by Nick Cardy and Bob Haney.
Major Story Arcs
Xen arrived on Earth and set after Aquaman, Aqualad and Mera. He initially used perfect duplicates of them against them. When this failed to do the job, Xen created giant-size versions of the trio. The giantic Aquaman and Mera still fell to their counterparts. but the giant Aqualad succeeded in capturing the miniature trio, mostly because they failed to pay attention to his presence.
On board the spaceship, the captured trio met other four captives - Blubber Man from the Waters of Jupiter, Fluorescent Water-Man from Mercury, Eel Man from the Plutonian Oceans and Shell-Back Man from the Lakes of Saturn. They worked together to steal Xen's duplication-gun and turning it against him, made an army of obedient Xens who defeated the original and were ordered to return all of the captives to their respective homes.
It remains unrevealed why he needs to capture the originals if he is able to make perfect duplicates of his specimens with his duplication gun.