Black Zero is a name shared by two supervillains, two terrorist organizations, one special forces group, and a computer virus that have all appeared in various comic book series published by DC Comics.
Superboy Villain
Black Zero was an alternate version of Superboy from a reality in which Superman never returned from the dead after his battle with Doomsday. This reality mirrored the main continuity with Paul Westfield, the Executive Director of Project Cadmus, secretly using his own cellstock for his team of scientists to immediately create a human clone that would be genetically engineered to look like Superman with powers deriving from a telekinetic field. Instead of the Newsboy Legion clones releasing him prematurely, the clone went through the full artificial maturation process to match the age of the original and became the new Superman. However, he believed that he was perceived as a usurper and resented by the people for not being the original Superman. After a battle with his reality's versions of Brainiac, Maxima, and Metallo led to the deaths of Supergirl, Brainiac and 318 civilians, a public backlash began against the new Superman and other clones that the people dubbed "genetix"; this led to Congress demanding the shutdown of Project Cadmus with the Guardian and the original directors of Project Cadmus sans Westfield abandoning the project.
After the Guardian was killed by an anti-genetix mob, the new Superman retreated to the original Superman's Fortress of Solitude and sought guidance from Kryptonian history. When he learned of the Black Zero clone liberation movement from Krypton, he discarded the name of Superman and took Black Zero as his new name. He decided to defend genetix everywhere and stop the anti-clone lobby by any means necessary. Turning Project Cadmus into Fortress Cadmus and creating an army of Guardian clones known as Stormguards with no previous memories of the original Guardian, Black Zero began a war in which most of his Earth's heroes were destroyed and cloned as soldiers for Cadmus with extreme changes by his head geneticist Dabney Donovan.
After conquering his Earth, Black Zero became aware of the existence of other realities when he encountered the Challengers of the Unknown, who arrived to his homeworld from a dimensional doorway. Metron of the New Gods, who appeared shortly after the Challengers, struck an agreement with Black Zero and offered him the chance to enter Hypertime via the construction of a reactor powered by the element Hyperium. Black Zero "rescued" other worlds in which he felt that genetix were being oppressed and left the conquered world's version of Paul Westfield in charge of the genetix on that world. The Challengers attempted to stop him by launching commando raids against Black Zero and his forces and smuggling themselves to whatever world was next in his crusade. To Black Zero's bafflement, the Superboys of these worlds often stood against him, leading him to store them in stasis chambers similar to the clone banks of Krypton. A Superboy from another reality that Black Zero tried to conquer escaped with a stolen Hyperjacket from Fortress Cadmus, but was shot with a laser by the Paul Westfield of his reality resulting in fatal burns. He warned the Justice League of the main continuity of Black Zero's coming before he died. Learning that the deceased Superboy was a genetic match and using the Hyperjacket repaired by the Gadget Guru of the Hairies, the Superboy of the main continuity traveled to other worlds where he learned of Black Zero and eventually landed on an Earth in which Superboy was Kal-El.
After Superboy was in possession of the hyperjacket, Black Zero followed him to each world that he visited, capturing all of the versions of Superboy that Kon-El encountered. When he reached the world of the Kal-El Superboy, he captured Krypto and ambushed both Kon-El and Kal-El using his Stormguard forces and his own powers. Learning that Superboy wasn't the Superboy that stole the hyperjacket, Black Zero sent him to Fortress Cadmus and revealed his true identity and told his story to Superboy via the latter in a mnemonic chair that showed parts of Black Zero's life in virtual reality. He revealed his plans to take over Superboy's reality, which he used a supposed anti-clone sentiment as justification, and to use one of the Doomsdays that he collected from alternate realities against Superman. After revealing his plan, a reformed version of Knockout from the deceased Superboy's world attacked with the Challengers of The Unknown, posing as Stormguards, and went after her reality's Paul Westfield. Westfield leaped into the Hyperium reactor and unknowingly erased every Paul Westfield in existence as well as himself. Angry at the loss of Westfield, who he considered a father figure, Black Zero sent Superboy, Knockout, and the Challengers to the Doomsday chamber to be destroyed while he prepared to take over the next world. Superboy and the Challengers escaped with Knockout making the ultimate sacrifice against the Doomsdays.
Black Zero was eventually defeated by a combined effort from Superboy, the Challengers of the Unknown, and all the other Superboys imprisoned at Fortress Cadmus. After Metron sends the Superboys and Stormguards back the their own realities along with immobilizing Black Zero with a Mother Box, he provides a ship for the Challengers and Superboy to fly through the hyperium reactor and into a hyperstorm to return home. Superboy intended to take Black Zero to his homeworld to keep watch over him, but Black Zero attacks the ship with his tactile telekinesis. Superboy dives into the hyperstorm and is almost struck by it until Black Zero rescued Superboy and saves the Challengers except for Matthew "Red" Ryan. Superboy attempted to convince Black Zero that his mission was wrong and to give people a chance, but Black Zero is engulfed by hyperstorm energy and disappears before responding to Superboy.
After his "death", Black Zero became a reminder to Superboy as to what could happen if he ever went out of control. During a battle with Etrigan over an enchanted armored gauntlet known as "Hyssa's Fist", Superboy puts on the gauntlet and while his strength increased, his costume was transformed into an exact copy of Black Zero's costume with the S-shield on the gold harness. He quickly used his tactile telekinesis to disassemble the gauntlet from his right hand.
Original
The original Black Zero appeared pre-Crisis in Superman (vol. 1) #205 (1968), in a story entitled "The Man Who Destroyed Krypton" written by Otto Binder with artwork by Al Plastino. This Black Zero revealed to Superman that he was a space saboteur who destroyed planets. He had been hired to destroy Krypton, and discovered that the internal stresses which would have destroyed it in any case were dying down, necessitating his involvement to ensure it exploded.
In the present day, Black Zero came to Earth, threatening to destroy it as he did Krypton. In desperation, Superman released Jax-Ur, a prisoner of the Phantom Zone, who wished to avenge Krypton's destruction. As he launched a devastatingly powerful missile toward Earth, Black Zero attacked Jax-Ur with a red Kryptonite bullet, causing his body to mutate wildly into several serpent-like forms. This proved to be Black Zero's undoing; While Superman saved the Earth from the missile, Jax-Ur transformed into a Medusa-like form, turning Black Zero to stone with his gaze. Black Zero's body was then shattered by Jax-Ur, in recompense for what he had done to Krypton.
This story suggests that were it not for something none of them knew, Jor-El would have been wrong and the Science Council right. E. Nelson Bridwell hypothesized that what Black Zero had noticed was the Green Lantern Tomar Re's attempts to prevent the destruction (as seen in Superman (vol. 1) #257 (1972)), meaning the two sets of interference canceled each other out, and Jor-El was right.
Organizations
The first post-Crisis version of Black Zero appeared in the 1988 World of Krypton miniseries written by John Byrne and illustrated by Mike Mignola. Although later described as a "clone liberation movement" in Superboy (vol. 3) #61, Black Zero was described as a "terrorist" organization that was ultimately responsible for the destruction of Krypton: in the Third Age of Krypton, Kryptonians extended their lives by maintaining clones in suspended animation (the Clone Banks), which they then harvested for body parts. Trouble in Kryptonian society concerning this issue emerged after it became publicly known that a prominent citizen raised a copy of herself in order to marry this clone to her own son. The enraged son publicly confronted his mother (after presumably killing the clone wife) and shot her, but was forcibly stopped from killing himself. After widespread public knowledge ensued concerning the fact that a clone was allowed to achieve full sentience as a living being, a new Kryptonian war began. Prominently featured in this war was the Black Zero organization, which acted against this "genetic slavery"; this began the War of Clone Rights, which lasted for a millennium. In their final act, Black Zero detonated a device that would later become known as the Destroyer. In essence, this device functioned as a giant nuclear gun, that fired a concentrated, sustained burst of nuclear energy directly into Krypton's core. Though subsequently destroyed by an ancestor of Jor-El himself, the Destroyer's effect would later be fully realized; It would cause a chain reaction deep within Krypton that would later obliterate the planet.
A second Black Zero group appeared in the 2005 graphic novel, Superman: Infinite City.
Most recently, the name "Black Zero" was used by an elite Kryptonian military force, under the command of Ursa. This unit included Thara Ak-Var's parents. The unit, except for Ursa, was killed attempting to defend Kandor from Brainiac.
Black Zero Virus
The Black Zero virus appeared in Superman Plus, a 1997 one-shot teaming Superman with the Legion of Super-Heroes. An intelligent computer virus created by the terrorist group, Black Zero II was dormant in the Kryptonian technology used to create the Fortress of Solitude. After being inadvertently activated by Apparition, Black Zero II ran Superman and the Legion through a warped version of Kryptonian history, intending to finish with the destruction of Earth. It was halted when Brainiac 5 inadvertently caused a power outage, and subsequently removed the virus from the Fortress' computers.