"He's the kind of character that says things that some people think, some people can't imagine thinking," the Hollywood star told Reuters.
"I've never read a character like it. I've never read a film like this."
The release of the satirical black comedy was celebrated with a royal premiere attended by Prince William and Princess Kate on Tuesday, after what actor Sandra Huller described as nearly 10 years of work by Oscar-winning director Alejandro G Inarritu.
The film has generated much anticipation since a trailer showed Cruise transformed into eccentric oil tycoon Digger Rockwell with grey hair, facial prosthetics and a padded bodysuit.
Cruise said this transformation was far from the most demanding aspect of the role, pointing instead to a 10-minute monologue filmed in a single take.
Anatomy of a Fall star Huller said it was "remarkable" watching Cruise's performance.
"It feels like all the things that he has learned in 46 years of acting have come into this character," she added.
In the film, Rockwell inadvertently triggers an ecological disaster that pushes the world to the brink of nuclear war before scrambling to save the planet.
But the filmmakers have revealed little else about the story, fuelling speculation about the plot and rumours it could be a musical, which Cruise has dismissed.
"If you experience the film without knowing anything about it, it's much better than if you (knew) before," Huller said, adding that the secrecy was not intended to create intrigue for its own sake.
While Cruise described the story as an exploration of "power and greed...responsibility and irresponsibility", Australian actor Sophie Wilde said it also carried a message about art being "a vessel for catharsis."
Inarritu, whose previous credits include Birdman and The Revenant, compared the process of making Digger to painting, saying every frame was carefully crafted to immerse audiences in the world of the film.
Digger will begin its global cinematic rollout on September 30.
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