The Eradicator was created by Superman's ancestor, Kem-L to preserve Krypton's purity (or at least his version of it) from being corrupted by alien influences. One such alien, the Cleric, took the device and left Krypton with his followers. The Cleric's followers died shortly after leaving as they were Kryptonian and bound to their homeworld.
The Cleric kept the Eradicator as he traveled the universe until a chance meeting with Superman on Warworld 200,000 years later. The Cleric feared for Superman's life as he had seen visions of his death at the hands of Mongul and used the device to escape Warworld. He noticed the device protected the last son of Krypton and healed his wounds. He eventually gave the device to Superman and passed away.
On Earth, the Eradicator caused a number of bizarre events in it's efforts to change Earth into a new Krypton. Superman threw the device into Antarctica, where it altered the ice to create the Fortress of Solitude, and used two scientists to create a portal to the Phantom Zone, where it drew Kryptonian artifacts to the Fortress. When Superman recovered the Eradicator, he discovered its xenophobic origin and its plan to transform Earth. It then erased his memory when he tried to stop it. Professor Emil Hamilton, who had previously examined the Eradicator, managed to restore Superman's memory. Superman then went into the Phantom Zone to stop the Eradicator's plan. There he encountered a projection of Kem-L and discovered that only Kem-L's descendants, the House of El, can control the Eradicator. First though, he had to undergo a rite of passage. When Superman completed the rite, he commanded the Eradicator to shut down and it returned to it's dormant state.
David Connor was created by Roger Stern for use in DC Comics. The Eradicator first appeared as a Kryptonian device in Action Comics Annual #2. The Eradicator later appeared in humanoid form for the first time in the Day of the Krypton Man story arc. He also assumed the identity of Superman in Action Comics #687.
Major Story Arcs
For More Information: The Day of the Krypton Man
While on Earth, in the process of transforming the landscape to be more Kryptonian, the Eradicator took on human form and was also known within the story arc as the Krypton Man. He had all the powers of Superman but none of his emotions. As the Krypton Man, he wore black and red Kryptonian garb.
Reign of the Superman
For More Information: Reign of the Supermen
When the "Man of Steel" died during his battle with Doomsday, the Eradicator placed Superman's body in a Kryptonian rejuvenation chamber and assumed Superman's appearance and identity. Superman eventually awoke, without his powers, to fight the team of the Cyborg Superman and Mongul. The Eradicator protected Superman by shielding him from a Kryptonite pulse that would have killed The Man Of Steel for good and used it to restore Superman's powers which seemed to kill the Eradicator. The body of the Eradicator was taken to S.T.A.R. Labs for examination but the Eradicator merged with Doctor David Conner who was dying of cancer.
Dr. Conner was now a human/Kryptonian hybrid but could not control the annihilation program and killed his wife and abandoned his children. The Eradicator joined the Outsiders and continued fighting evil.
For More Information: Adventures of Superman
Dr. Conner's realized that somehow the Eradicator had split in two, one halve stayed with the hybrid and the other merged with the ash from the Fortress of Solitude becoming a Kryptonian warsuit. Conner, having allowed himself to be absorbed and briefly gaining control, blasted himself into space vowing never to return, a vow he has failed to keep.
The Eradicator/Conner gestalt returned, greatly changed, to warn Earth's heroes about the approach of Imperiex.
Return To The Outsiders
For More Information: Outsiders
After the "death" of Batman, Geo-Force eventually takes over leadership of the team. Geo-Force had been acting a little irrationally after his battle with Deathstroke. Without consulting the rest of the team, he orders them to attend a press conference he delivers to the people of Markovia.
He announces that he has entered into a non-aggression treaty with the people of New Krypton. While the Kryptonians have been banned from Earth, Geo-Force offers them a safe haven in his country. Eradicator has return as the representative of New Krypton.
Reign of Doomsday
For More Information: Reign of Doomsday
During the events of the Reign of Doomsday, Doomsday seeks vengeance against Superboy, Steel, Cyborg Superman and Eradicator for their rise up after the apparent death of Superman the four that rose up in the arc Reign of the Supermen. Doomsday defeats the other members of the outsiders easily leaving just Eradicator. Eradicator is impaled and seemingly killed by Doomsday in Outsiders #37. Doomsday then leaves the scene and takes Eradicator's body with him.
It is later seen that Eradicator, Supergirl, Superboy, Steel and Cyborg Superman had all been captured by Doomsday and brought to a space station in the debris of Krypton. It is here that Eradicator, Superman and the other captives find out the terrible secret of The Doomsdays.
Eradicator's body is completely destroyed by Doomslayer. His energies possess the body of Doomsday and he leads the charge into battle.
Powers & Abilities
Eradicator's body is a genetic replica of Superman's. As such he has similar powers such as incredible super strength, the ability of flight, the ability to produce heat blasts from his eyes, nigh invulnerability as well as the enhanced senses that Superman possesses such as super acute hearing and super acute sight.
Eradicator unlike Superman has the ability also to absorb and release energy out from his hands in the form of very powerful energy blasts. Being that he is basically a piece of Kryptonian computer software he has computer like analytical abilities, he is capable of processing, analyzing and computing a situation very fast. Eradicator is also very intelligent.
After Eradicator fought Mr. Majestic, during the time when Mr. Majestic was trapped in the DC Universe. Mr. Majestic reprogrammed him. It was never explained for what reason or what difference this reprogramming made but it may bare some bearing in the future.
In other media
Legion of Super Heroes
For More Information: Legion of Super Heroes
The second season of the Legion of Super-Heroes television series featured a future version of Superman alongside the Clark Kent versions. This second Superman, called Kell-El or Superman-X, is a clone of the original Superman from the 41st century who was bred for fighting.
The character is based on the Kon-El Superboy, Lar Gand, and even the Eradicator. In the series Kell-El's personality is very similar to the Eradicator in his ''Last Son Of Krypton'' phase.