<P> The plots of the television and radio series are more or less the same as that of the first two novels, though some of the events occur in a different order and many of the details are changed . Much of parts five and six of the radio series were written by John Lloyd, but his material did not make it into the other versions of the story and is not included here . Many consider the books' version of events to be definitive, because they are the most readily accessible and widely distributed version of the story . However, they are not the final version that Adams produced . </P> <P> Before his death from a heart attack at age 49 in 2001, Adams was considering writing a sixth novel in the Hitchhiker's series . He was working on a third Dirk Gently novel, under the working title The Salmon of Doubt, but felt that the book was not working and abandoned it . In an interview, he said some of the ideas in the book might fit better in the Hitchhiker's series, and suggested he might rework those ideas into a sixth book in that series . He described Mostly Harmless as "a very bleak book" and said he "would love to finish Hitchhiker on a slightly more upbeat note". Adams also remarked that if he were to write a sixth instalment, he would at least start with all the characters in the same place . Eoin Colfer, who wrote the sixth book in the Hitchhiker's series in 2008--09, used this latter concept but none of the plot ideas from The Salmon of Doubt . </P> <P> In The Hitchhiker's Guide to the Galaxy (published in 1979), the characters visit the legendary planet Magrathea, home to the now - collapsed planet - building industry, and meet Slartibartfast, a planetary coastline designer who was responsible for the fjords of Norway . Through archival recordings, he relates the story of a race of hyper - intelligent pan-dimensional beings who built a computer named Deep Thought to calculate the Answer to the Ultimate Question of Life, the Universe, and Everything . When the answer was revealed to be 42, Deep Thought explained that the answer was incomprehensible because the beings didn't know what they were asking . It went on to predict that another computer, more powerful than itself would be made and designed by it to calculate the question for the answer . (Later on, referencing this, Adams would create the 42 Puzzle, a puzzle which could be approached in multiple ways, all yielding the answer 42 .) </P> <P> The computer, often mistaken for a planet (because of its size and use of biological components), was the Earth, and was destroyed by Vogons to make way for a hyperspatial express route five minutes before the conclusion of its 10 - million - year program . Two members of the race of hyper - intelligent pan-dimensional beings who commissioned the Earth in the first place disguise themselves as Trillian's mice, and want to dissect Arthur's brain to help reconstruct the question, since he was part of the Earth's matrix moments before it was destroyed, and so he is likely to have part of the question buried in his brain . Trillian is also human but had left Earth six months previously with Zaphod Beeblebrox, President of the Galaxy . The protagonists escape, setting course for "The Restaurant at the End of the Universe". The mice, in Arthur's absence, create a phony question since it is too troublesome for them to wait 10 million years again just to cash in on a lucrative deal . </P>

When was hitchhiker's guide to the galaxy published