 A central theme of this version of the Superman mythos was that the character was to remain the last surviving remnant of Krypton.Thus, Silver Age elements such as Supergirl, Krypto, and Kandor had never existed in this version (though Post-"Crisis" versions of these elements were eventually reintroduced).The supervillain Doomsday was revealed in the 1990s as a being genetically engineered by Bertron, an alien scientist, on an ancient Krypton.