Douglas Adams' comic science fiction book series, 'The Hitchhiker's Guide to the Galaxy', was published as a "trilogy in five parts", with publication spanning 1979 to 1984. The novels also inspired 3 British radio series, a TV series, and a feature film. Adams' works have gained a cult following. In particular, the joke response to "life, the universe and everything" often serves as a secret geek handshake.

The series starts with British earthling Arthur Dent learning that his girlfriend is abducted by aliens and that Earth is to be demolished by bureaucratic alien lifeforms, known as the Vogons, to make way for a "hyperspace bypass". Arthur and his alien friend, Ford Prefect, hitch a ride on a Vogon spaceship just before Earth's destruction. Zany adventures ensue across the galaxy and beyond.

The protagonists learn of a planet-sized supercomputer which had been designed to answer to the "Ultimate Question of life, the universe and everything". The computer, named Deep Thought, worked on computing the answer for 7.5 million years.

The TV series image shows the moment when Deep Thought finally reveals the all-important answer at a great ceremony after the 7.5-million-year calculation: "I thought it over quite thoroughly. It is 42."

"Why 42?" many have since wondered. According to Adams himself: "It was a joke. It had to be a number an ordinary, smallish number, and I chose that one...I sat at my desk, stared into the garden and thought '42 will do'...End of story".

More Info: en.wikipedia.org