The DC Universe (or simply DCU) is an alternate universe from the realms of Mortal Kombat that are inhabited by courageous men and women known as super heroes, some endowed with superhuman capabilities, that combat forces of evil. Conversely, men and women with extraordinarily evil intentions, mostly called super villains, operate in an opposite capacity, and mass conflicts arise between the two. The DCU is a shared universe, where most of the comic stories published by DC Comics take place. The fictional characters Superman, Batman, and Wonder Woman are well-known superheroes from this universe.
About the DC Universe
For a more comprehensive guide, see the Wikipedia page for the DC Universe.
Because of the expansive nature of DC Comics, the history of the DC Universe is highly extensive and reaches from the beginning of time into the vast reaches of the future, and spans from Earth through the vastness of the universe. The Earth in the DCU is considered between 15% and 20% larger than the actual planet Earth, to make room for the numerous fictional nations and cities that are present there.
Golden Age
The most notable components of DC Universe history revolve around the masked adventurers of Earth that began appearing in major cities in the 1940's. The first superhero team, the Justice Society of America, appeared consisting of heroes like the first Flash, Hawkman, the original Green Lantern, and Wildcat. This ushered in what would be known as the "Golden Age of Heroes."
The JSA continued to exist and contribute to the war effort in Europe, and operated through the 1950's until they came under attack by United States Senator Joseph McCarthy, who alleged through the House Un-American Activities Committee that masked adventurers may have ties to communism. In protest, the JSA disbanded, and wouldn't be heard from for a very long time. Super heroes would also disappear from the Earth for several years, until an orphan from another planet emerged as Earth's greatest hero.
Silver Age
With the arrival of Superman in Metropolis, a new age of heroes was born. Whispers of a dark, merciless urban vigilante surfaced from Gotham City as Batman burst onto the scene next to begin his war on crime. The Amazonian princess Wonder Woman also appeared and joined the fight against evil. In Central City, the second Scarlet Speedster, the Flash made his presence felt, and the first human member of the Green Lantern Corps, Hal Jordan, became a guardian of Earth as well. A new generation of a faction of heroes, the Justice League, emerged from the unity of these new heroes, and the forces of evil would have to combat the world's greatest heroes every time the Earth was threatened.
But with a torrent of good that the Silver Age would bring, the heroes would do battle with a new generation of villains as well. From the day Superman appeared, the self-righteous and obsessive mogul Lex Luthor would oppose him to prove to himself and the world at large that humanity should not look to an alien for salvation. With the driven and focused mission of the Batman, came the equal and opposite reaction of the intense, deranged, and chaotic existence of the Joker. The burglar Catwoman would skirt the line between good and evil, and the assassin Deathstroke would prove formidable to any hero that would stand in his way.
It is these battles between the forces of good and evil that have defined the DC Universe for as long as it has existed, but as with every intense force of evil, the heroes of the DCU have proven that they will never stop defending what is right.