The Dragon is a metaphor for hope and justice in a world where there is no hope and never will.
It is easy to disregard the Dragon if suffering is not a part of your daily life.
Let's imagine those who say there is a dragon living in their garage contend that the dragon is a required salve for the harms of living in a hostile world. Though I can not prove (though still approaching with an open mind) the physical existence of a dragon in anyone's garage, I can not argue against the proclaimed effect on those who find their suffering abated. That is, the effect is real if you say it is; the dragon is not.
Demon-Haunted World is about skepticism, and how to use science and rational inquiry to avoid scams, pseudoscience, hoaxes, and possibly religion. It is not a strictly atheist book, although you could read it as one if you tilt your head properly.
But how can you not know anything else about Carl Sagan?
He wrote many books popularizing science, including Contact, The Dragons of Eden, Broca's Brain, and Cosmos. He also co-wrote and hosted the series Cosmos on PBS, which is the most-watched PBS show in history, and well worth watching on DVD.
He was founder and first President of The Planetary Society (http://www.planetary.org/). He was an avid supporter of SETI. He assembled the gold plaque that went into space on Pioneer 10, and the golden records that went out on the Voyager probes.
As an astronomer, he made several important hypotheses about the structure of other planets, particularly Venus, and drew connections between Venus and Earth-based global warming and greenhouse emissions.
He was active in investigating UFO claims, including serving on the Ad Hoc Committee that reviewed the Air Force's Project Blue Book. He was convinced of the probability of extra-terrestrial intelligence, but equally convinced that we had not encountered it yet.
Most importantly, he brought us the phrase "billions and billions", even though he never said it himself until long after it was a joke.
Here's a collection of quotations: http://en.wikiquote.org/wiki/Carl_Sagan
And one for the road: "If you wish to make an apple pie from scratch, you must first invent the universe."