How did it go from Allen Klein and Alejandro Jodorowsky to Just Jaeckin?

I recall having read about this, too. Apart from that, I'm no wiser about it than you, I'm afraid.

Here are some other interesting snippets to add to this topic. These directors have all been mentioned in O-related terms.

- Henri-Georges Clouzot was interested in doing an adaptation for many years.

- Ken Russell is said to have been considered for the 1975 version before Jaeckin came on board (as mentioned in Michael Weldon's Psychotronic Video Guide, but I haven't seen it elsewhere)

- In the early 90s, Lars von Trier seriously considered a full-feature adaptation. He even contacted Philippe d'Argila, the son of Pauline Reage/Anne Desclos, in order to negotiate the rights. Unfortunately, d'Argila had seen von Trier's film The Element of Crime and did not like it at all. Thus, no deal.

- A countryman of von Trier, Dane Henning Carlsen (famous for his adaptation of Knut Hamsun's Hunger, 1966), worked quite a bit on an adaptation of Return to the Chateau, Reage's sequel, to be called A Girl in Love. It was to have been shot in French around 1976-77, but nothing came out of it.

Christopher lee turned down the role as Sir Stephan. He made the man with the golden gun two years before and in one scene he looked pretty menacing and I’m guessing this is the scene the producers saw that made them want him as Stephan. Personally I think he would have made a much better Stephan than the foppish looking Steel. But I also bet most movie goers wood l confuse the story of O with a run of the mill hammer horror movie. If he was in it.