More hints: It inspired three movies and a graphic novel.
EDIT: And it is an opening line. (I thought that was required until I reread the first post.) So my signature itself is from a reasonably well-known book that inspired a movie. It is not a first line.
Quite possibly the most iconic opening of a book in the English language! It's Moby Dick, or The Whale. Couldn't stand it in high school, but always thought I should give it another try. (The endless descriptions of the whale really tested my adolescent patience. )
Here's one:
"Tell me, Muse of the man of many ways, who was driven
far journeys, after he had sacked Troy's sacred citadel."
Then was the king wonderly wroth. And then the king sent him plain word again, and bade him be ready and stuff him and garnish him, for within forty days he would fetch him out of the biggest castle that he hath.
It befell in the days of Uther Pendragon, when he was king of all England, and so reigned, that there was a mighty duke in Cornwall that held war against him long time.
Then I would have to guess Chretien de Troyes or Geoffrey of Monmouth. I think Geoffrey wrote more about Arthur himself, while Chretien wrote about those around Arthur. I'd go with Geoffrey, but don't have a title.