Adams had recently graduated from Cambridge, where he'd written and performed sketch-comedy to little or no acclaim. He had made a few friends there, among them Simon Jones, who went on to play Arthur Dent in the radio and television versons of The Hitchhiker's Guide to the Galaxy, and Graham Chapman, one of six Monty Python players who had begun writing comedy with then classmate, John Cleese.
At 24 years of age, he'd already considered himself a failure as a comedy writer, when he pitched the idea for Hitchhiker's to a BBC radio producer. It was accepted. It was 1977. Nobody had any idea what they had started, least of all Douglas Adams.
By the airing of the sixth episode, Hitchhiker's had become a national phenomenon with a large cult following that was not only science fiction and radio fans (Hitchhiker's was the first comedy series to be produced in stereo), but a huge portion of the general public who had stumbled upon this hilarious story.
In Don't Panic, Neil Gaiman examines the evolution of The Hitchhiker's Guide to the Galaxy in its various incarnations as a radio series, television series, L.P. record, computer game, interactive fiction, and most importantly, as the legendary five-book trilogy. Don't Panic was originally published in 1988 and is now in it's third edition. A huge Hitchhiker's fan, Neil Gaiman's research for the book included extensive interviews with Douglas Adams, and the book is consequently full of interesting quotations and anecdotes about the history of H2G2.
Douglas Adams died of a heart attack in 2001 at the age of 49. Don't Panic is not his biography. If you're looking for a biography of Douglas Adams, check out Wish You Were Here by Nick Webb, Adams' longtime friend and editor back when he was first signed by Pan Books. Don't Panic is a detailed historical reference to the evolution of The Hitchhiker's Guide to the Galaxy, which I would recommend the casual fan pass by.
Conversely, zealous H2G2 enthusiasts navigating their way through the various wrinkles of Adams' creation will likely find Gaiman's book essential to their travels and deserving of prominent space in their backpack, right next to their towel.