Originally known as the League of Life, the Black zero movement was a gruop of people from the planet krypto who questioned the use of clones to preserve the integrity of the kryptonians citizens. Lead by Sen-M, they plead for the same rights for clones as for natural born kryptonians. The massive use of clones as spare parts was imoral for the members of the league but their efforts were not hear for most of the kryptonians. The few who choose not to follow the custom to use clones for keep them alive eventually died by sickness or old age and the league apparentely died with them.
However the ideal of the league did not were forgoten. Thousand years later, the kryptonian youth questioned again the use of clones, this time with a more radical and agressive attittude, not only critiquing the use of clones but demanding the end of all kryptonian life for the crimes of previous generations. This movement, oppossed to themore conservative kryptonian sectors, would lead to a planetary civilwar where most of Krypton landscape was wasted. The last members of Black Zero would be defeated by Van-L, who thwarted a scheme to destroy the planet and finally ended the war, implementig a new way of life where clones would be not necessary.
In an alternate universe, Black Zero is a grow-up clone of Superman, analog to Kon-El who had to face the reject of society for his clone status. learning about the black Zero histoy, he took the name as his new moniker, starting campaigne whcih would lead him to clash with the Challengers of the Unknown and with ths Superboy from the main universe.