As you can see, the consensus seems to be "Holy Sh$#!"
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Batman: The Dark Knight Returns is a four-issue comic book limited series written and drawn by Frank Miller, originally published by DC Comics under the title Batman: The Dark Knight in 1986. When the issues were released in a collected edition later that year, the story title for the first issue was applied to the series as a whole. The Dark Knight Returns tells the story of a 55-year-old Bruce Wayne who comes out of retirement to fight crime, only to face opposition from the Gotham City police force and the United States government.
A sequel (made again by Miller), The Dark Knight Strikes Again, was published in 2001.
The upcoming Christopher Nolan film The Dark Knight Rises has been confirmed to take up the action eight years after the events of The Dark Knight, and involves a retired Batman coming back to take up the mask once more.