According to Ray Bradbury:
Back in 1950, I dined out one night with a friend. Later in the evening we were walking along Wilshire Boulevard when a police car stopped and an officer got out and asked us what we were doing.
“Putting one foot in front of the other,” I said, not very helpfully.
The policeman kept questioning us as to why we were being pedestrians, as if by taking a late-night stroll we were coming perilously close to breaking the law. Irritated, I went home and wrote a story called The Pedestrian.
Several weeks later, I took my pedestrian out for a literary walk where he encountered a young girl named Clarisse McClellan. Seven days later, the first draft of The Fireman was finished.
Some years later, looking back I thought The Pedestrian was the true source of Fahrenheit 451, but my memory was incorrect. I now realize other things were at work in my subconscious.
It is only now, some 50 years later after that L. A. police officer challenged my right to be a pedestrian, that I see the odd ideas that rose to perform in short stories, which went unnoticed as I wrote them.
I wrote a tale about the greatest fantasy authors in history being exiled to Mars while their books were burned on earth. That became a short story called The Exiles. I wrote another tale, Usher II, in which my hero complains that he, as a fantasy writer, is rejected by the intellectuals on earth who make fun of the grotesques that sprang up in the tales of Edgar Allan Poe and other similar authors.
And years before that, I published another novella, called Pillar of Fire, in which a dead man rises from the grave to reenact the strange lives of Dracula and Frankenstein’s monster.
All of these stories were forgotten when I first wrote Fahrenheit 451. But they were still there, somewhere, percolating in my subconscious.
In the case of the final version of Fahrenheit 451 … I brought all my characters onstage again and ran them through my typewriter, letting my fingers tell the stories and bring forth the ghosts of other tales from other times.
From the introduction to the graphic novel of Fahrenheit 451.