Kenneth More was originally cast as Samantha Eggar's secret lover but all of his scenes were cut from the final print.
Natalie Wood turned down the role of Miranda Grey.
According to Samantha Eggar, "The ending of The Collector, in fact, is almost illegal, because the Stamp character, Freddie Clegg, gets away with murder, and you weren't allowed to do that in those days." However, John Trevelyan, the censor, who had recently married a woman about half his age, nodded off during the screening, and never saw the ending of the film. He woke up and signed off on it. Had he been awake, we might have had a very different film, or people "might have been arrested".
According to Terence Stamp, Wyler wouldn't let Samantha Eggar off the set during the day. He also wouldn't allow her to eat with anyone else during the lunch break. Stamp argues Wyler knew what he was doing, as the director whispered to him one day on set, "I know this looks cruel, but we're going to get a great performance out of her."
According to John Fowles, the original cut of The Collector ran more than 3 hours.
According to Book "The Unkindest Cuts: The Scissors and the Cinema," William Wyler hated to cut this film and Kenneth More's entire co-starring role. Wyler said: "Some of the finest footage I ever shot wound up on the cutting room floor, including Kenneth's part."
According to the Book "Searching for stars: stardom and screen acting in British cinema", Kenneth More was unhappy when he found out that his scenes were completely cut from this film.
Even though Samantha Eggar was unhappy with Stamp's cold treatment of her during filming, she couldn't have known that he was simply following Wyler's instructions and staying in character. Stamp later said, "All the guys had crushes on her, she was so beautiful... I had a crush on her, too, and I was friendly with her. But when we started the movie, Willy said, 'I don't want you to have anything to do with her.' He wanted me to withdraw any friendship. He didn't want her to have anywhere to go or anyone to talk to, except her coach. He didn't want her to be able to come to me in the evening and say, 'God, it's so awful.'"
For the sequence in which Freddie drags Miranda through the rain, William Wyler had prop men throw buckets of water over Samantha Eggar without warning between takes. Eggar later spoke of how Wyler succeeded in making her feel "defenseless," hence deepening her performance.
In the kitchen a calendar is shown for the month of May. The film was made in 1965, however the month of May shown corresponds to 1966. This most likely was done for the purpose of using the year the film was projected to be widely viewed.
Originally the film was to be made in black and white.
The story makes constant reference to Shakespeare's play "The Tempest". In "The Tempest" Miranda is Prospero's daughter. Fred Clegg also refers to himself as "Ferdinand", or "Ferdie" to disguise his identity. Ferdinand is the name of Alonso's son in the play. Miranda, however, calls Fred "Caliban", who is an ugly misshapen dwarf in the play.
This film was cited by notorious serial killer Bob Berdella as a key inspiration for his crimes.
Two small cut scenes were used in the film's theatrical trailer. The first scene is where Samantha Eggar is talking with her left hand on the back of the head. The second scene is where Samantha Eggar is sitting right next to a window and it's raining outside.
When Freddie is stalking Miranda she walks by a cinema that shows that Ben-Hur is playing. Director William Wyler also directed Ben-Hur.
While the film is overall faithful to John Fowles' novel, the scene where Freddie's neighbor comes over and Miranda tries to get his attention by flooding the bathroom was created for the film and was not in the novel.