The Collector of Worlds is an alien android who seeks out and preserves a portion of doomed worlds.
The Collector of Worlds takes the form of humanoid robot with green skin. However, that is not his only body; his intellect allows him to control many Coludroids at a single time.
The Collector of Worlds has a cool and calculating mind. Because his twelfth-level intellect grants him tactical prowess over his less-intelligent foes, he can come across as rather smug and arrogant. He is driven by a directive to preserve the untainted culture of doomed worlds, and accomplishes this by shrinking one of their representative cities and enclosing them in bottles aboard his ship. As such, although his actions can be viewed as villainous, the Collector is not malicious and can be reasoned with.
The Collector moved his ship to Metropolis, and hovered above downtown. He initialized his plan by launching a probe at the city, which quickly tunneled deep underground. The device created a force field that cut through everything, including bridges, and cut off all communications. The encasement of Metropolis into a bubble was completed in minutes.
The Collector activated an energy beam from the bottom of his ship, targeting the force field around Metropolis.
Metropolis December 1, 17:45EST
The Collector anticipated the arrival of Martian Manhunter, the Atom and the Flash aboard his vessel, and descended toward them on a platform, informing them of their intrusion. When questioned about his presence, he listed his many names, until finally introducing himself as the Collector of Worlds. He proclaimed it was futile to prevent him from preserving Metropolis. The Collector intercepted a direct attack from the Flash, before being telekinetically levitated by Martian Manhunter, who attempted to disable his systems. However, the Collector's reinforced skeleton proved to be too powerful to dismember. The Collector stated he was aware of Manhunter's distraction, and casually dropped the Atom from his grasp. After making quick work of the three heroes, the Collector opened a hatch beneath the Leaguers, sending them plummeting from his vessel.
Blue Beetle's scarab adjusted to his attack; together with Sphere, he attacked the Collector. For a short period of time, the alien was taken aback by the presence of a New Genesis life-tech on such a primitive world, and felt Blue Beetle's participation was ironic. Nevertheless, he did not deviate from his plan to preserve a piece of Earth.
The Collector's Ship December 1, 19:01EST
Alpha Squad renewed the attack, but the Collector was protected by a forcefield. Reinforcements suddenly teleported in. As soon as Nightwing briefed them on the situation. Lagoon Boy destroyed the Collector's body with the Bio-Ship. Superboy picked up the intact head of the robot, and was surprised when it remained functional. The Collector recognized Conner's partial Kryptonian heritage, and shot him in the face with a green scanning beam.
Metropolis December 1, 19:03EST
The Collector remarked that Superboy was a clone whose Kryptonian DNA was corrupted. Superman countermanded his assessment, and incinerated the head with heat vision. But the body that was destroyed was merely one of many. Dozens more Coludroids of the Collector appeared, and pondered how one pure Kryptonian could have survived. He cut himself off when he noticed something wrong with the probe embedded under Metropolis, which was being sabotaged by Bumblebee and Beast Boy.
The Collector warned the heroes that if the force field were to be shut down while the shrinking beam was active, the planet would be destroyed. Nightwing advised him to shut it off, and he agreed. He was a collector of worlds, and not a destroyer. The Collector turned off the beam, and inquired if the Justice League and the Team would continue to oppose him. When they answered in the affirmative, he decided that the survival of one Kryptonian could mean the need to collect is not absolute.
Metropolis December 1, 22:03EST
After reversing the effects of the shrinking ray on Metropolis, the Collector's ship departed from Earth.
Powers and abilities
The Collector of Worlds is among the most intelligent and technologically advanced beings in the entire galaxy.
Energy weapons: The Collector is able to shoot green energy beams from emitters in his chest and arms.
Force field: He can generate a spherical force field around himself.
Invulnerability: His reinforced bryaksium skeleton protects him from telekinetic attacks, and bodily harm.
Microscopic vision: The Collector was able to see the Atom and prevent him from reaching his innards; this is presumably how he was also able to tell that Conner was part-Kryptonian.
Super strength: The Collector was able to hold off the likes of Martian Manhunter, the Flash, Blue Beetle, and Sphere without showing any stress. 
Super intelligence: The Collector possesses a twelfth-level Coludroid intellect that allows him to predict the movements of any individual directly.