The Warworld

The Warworld is an artificial satellite previously helmed by Mongul. It possesses innumerable armaments capable of devastating a planet and warding off attackers, as well as drones for internal security and upkeep. It requires a crystal key to become operational.

Early history
According to the Reach, the spaceship was created by a now extinct race. Mongul acquired the key after being driven off his home planet by another despot.

2016
It appeared after an unknown amount of time in the Solar System, where it was detected by the Watchtower's sensors. The visual feed showed that object was about to pass in front of Rhea, but when Nightwing realized was actually behind Saturn's moon, he was astonished by its size.

Background in other media

 * This version of Warworld, complete with crystal key and control chair, was based on the pre-Crisis version introduced in DC Comics Presents #27.  In the comics, it was created by a warlike race of aliens called the Warzoons, who died off from the mental strain of controlling Warworld.  A pacifist alien race called the Largas found the weapon, and created a crystal key to unlock the artificial planet.  The key found its way to the Martians, and was stolen by Mongul.