Since hatching Alien 33 years ago, Ridley Scott has hoped no other filmmaker would try to answer this question: Where did the space eggs containing those terrifying beasts come from?
Scott has hints of an answer himself with Prometheus, a cousin to Alien that opens tomorrow and marks the filmmaker's return to science fiction.
His origin story raises as many questions as it answers about the derelict space ship where humans discovered the eggs that unleashed such horror in the 1979 film and its three sequels, along with two hybrid Alien vs. Predator films.
Other directors - James Cameron on 1986's Aliens, David Fincher on 1992's Alien 3 and Jean-Pierre Jeunet on 1997's Alien Resurrection - had carried on with Scott's creation. And while Scott veered away from science fiction after 1982's Blade Runner, he always wondered if there might be a fresh way back into that Alien universe.
"At the end of the Alien franchise, when all was said and done with the fourth film, it seemed to me you can't use that creature one more time. It was too familiar and no longer frightening. Therefore, is it over?" Scott said.
Yet fans have wondered for decades about that fossilised "space jockey" depicted in Alien, the apparent pilot of the extra-terrestrial wreck that Ripley (Sigourney Weaver) and her crew stumbled across. Who was he, what was he, where did his cargo of alien eggs come from, and where were they bound?
"I remember from the very first Alien, there was one overriding question no one had addressed in any of the four," Scott said. "I kind of sat on it, hoping it wouldn't come up."
Some of the secrets are revealed in Prometheus, which stars Noomi Rapace, Michael Fassbender, Guy Pearce and Charlize Theron as explorers who set out to find the "engineers" that created humanity but discover that those makers have terror in store for their offspring.
The "P" word - prequel - has been tossed about to describe the new film. But Prometheus is more a precursor than a straightforward prequel to Alien.
"To call it a prequel is limiting, but it does have a connection," Guy Pearce said. "It basically plants the seed for that original Alien film, but it's a really clever way to go about it, looking at this mission we're actually on and how it does connect with that alien creature that Ripley does find."
Set in the late 21st century, a few decades before the action of the original film, Prometheus exists in a world familiar to that of the Alien franchise - with a monolithic corporation, space explorers in hibernation chambers for their long journey, an enigma of an android whose motivations keep the crew - and the audience - guessing.
And, of course, loads of nasty creatures, in far greater variation than in any of the "Alien" movies.
"There are elements of a world he created that are definitely similar. But that doesn't make it a prequel," Theron said. "I felt like this was a standalone film. This film asks really big questions that were never asked in Alien. Age-old questions of who our creators are, what would they look like, what would they want from us? What would we want from them?"
Theron plays the ice-queen overseer of the company backing the voyage, Pearce is the corporation's patriarch, Fassbender's the inscrutable android with agendas all his own, and Rapace is something of an update of Weaver's Ripley, an idealistic scientist forced to become a bad-ass action hero.
Like Alien, Prometheus has ghastly, gory moments as creatures infiltrate human hosts. Rapace is the focus of the film's most memorable moment, one to rival the shock of the infant alien bursting from John Hurt's chest in the 1979 original.
"It's something that's literally under your skin and already makes you feel kind of queasy," Fassbender said. "Then to see it on screen. It's kind of a sick fantasy to have, but with any luck, millions of people will be suffering nightmares from that hectic scene in the middle with Noomi."
Rapace spent about a week shooting that scene, and it gave her nightmares herself.
"I was a complete mess," Rapace said. "I even had a dream that I woke up from a nightmare holding my tummy and thought, something was moving in there, and thought, oh my God, this cannot be happening. I better call someone, and the first thought was to call Ridley. He'll know what to do."
Scott knows what he'd like to do now with Prometheus: Make a sequel.
There are no simple answers at the end of the film, which sets the characters and the audience up for even bigger questions to ask in the next chapter.
A Prometheus follow-up might explain more of the connections to Alien, but this first film is more of a taste or a teaser on how the two stories fit together.
"That would be too linear, too neat. That would be like a jigsaw puzzle, putting all the pieces in place," Scott said. "It's like doing Blade Runner again. You can't just pick up where you left off and continue. You have to ask how we can rework this into the universe we live in 40 years on."