Doppelganger
A prominent trope among several forms of media including comic books. The Doppelganger denotes a villain who is nearly identical to the hero in many ways, including background, personality and powers, but uses his abilities for evil rather than good. In some cases, this is used to show the reader what the hero could have become. In others, the Doppelganger serves as a thematic foil for the hero.
Earth-0
Also known as NEW EARTH and PRIME EARTH, this world is the foundation stone of the Multiversal structure. It has survived several attacks, surgeries and reconstructions on the way to its current form. On Earth-0, the greatest young superheroes of the age are at the peak and pinnacle of their powers and achievements.