Warning: Minor spoilers ahead for Avengers: Infinity War.

In a bare white room in Atlanta's Pinewood Studios in 2017, visual effects guy Matt Aitken held in his hands the entire script to Avengers: Infinity War. It was incredibly rare. So rare, some of the movie's biggest stars didn't have it. So rare, a Marvel representative had to supervise him.

Aitken was different. He was a supervisor at effects company Weta, leading a team brought on to create one of Infinity War's most pivotal scenes: the moment where Thanos battles a hit squad of Marvel superheroes, including Iron Man, Spider-Man and Star-Lord.

Weta Digital

The scene is already iconic. Spider-Man pulls Thanos one way with his ultra-strong web, while Iron Man and Drax attempt to yank off the universe-destroying Infinity Gauntlet on his other hand. Mantis, propped on his head, induces his brain into a trance state. The complex battle scene utilizes the skill sets of eight characters including the reality-bending Thanos.

In Aitken, directing duo the Russo Brothers had found their guy. The New Zealander's credits included an Academy Award nomination for visual effects for 2009's District 9, and extensive work on Iron Man 3 in 2013.

His team at New Zealand-based Weta Digital, the digital visual effects company behind Avatar and Lord of the Rings, consisted of 400 people, rising to 800 at times. They also worked in conjunction with another effects house, Digital Domain -- not to mention the other eight effects companies Marvel employed from London, Vancouver, California and across the world. Under the watchful eye of the movie's visual effects supervisor Dan DeLeeuw, these multiple effects companies conjured the movie's 2,800 scenes, essentially all of which contain CGI.

Aitken says the directors were keen to work closely with Weta. They were "very keen to get on the phone with us," he says, "and sequence-by-sequence talk us through their goals and their visions for those sequences and potentially nuances of the character beats. That was a little bit unusual as far as Marvel movies go, in my experience."

Marvel/Jennifer Bisset/CNET

It was this opennes that led to Aitken reading the script in full -- an honor not afforded even to some members of the cast. Aitken's desire to see the entire script came down to "context," he says: "I needed that overall understanding of how the story has to plan out."

The reason for the "incredibly tight" security in the first place involved "a major thing that happens at the end of the film. They wanted to make sure that when people went to see the film, they were able to enjoy that as a fresh experience."

Weta's task was to capture the barren orange landscape of a once beautiful planet ravaged by overpopulation, which motivated Thanos' quest for the Infinity Stones. Aitken and his team not only had to shape a planet that didn't "look too stylised," but had to create believability in a character portrayed entirely through digital effects.

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"We tried to make a more natural-looking Thanos as opposed to the more cartoonish-looking Thanos that appeared earlier," he says. Thanos' first appearance came in The Avengers in 2012, where he looked more like his comic book counterpart.

"By making him more human in his facial appearance, we could empathize with him more, which was important if we were going to spend all this time with that character."

Marvel Studios

With the battle scene, Aitken says, "we were able to go a bit crazy." One section of the fight features Thanos leaping across floating chunks of rock. Dr. Strange attempts to attack him with golden lightning. The team designed it so that when the rocks are hit, they explode into great splashes of lava.

The production built a set representing Titan on the largest shooting stage at Pinewood. They shot for weeks with actor Josh Brolin doing motion capture for Thanos, so they could "essentially superimpose digital Thanos over the footage of Josh."

Marvel Studios

As for the other actors in the scene, including Robert Downey Jr., Benedict Cumberbatch and Chris Pratt, Aitken got a taste of dealing with an A-lister's busy schedule.

"Scheduling the A-list actors all at the same time meant that sometimes, when you think you're looking over Dr. Strange's shoulder onto Tony Stark, it might not actually be Benedict Cumberbatch's shoulder that you're looking over. That was purely for availability reasons."

All the hard work was worth it. "The work in it is so dense that people are going to see new things if they go a second time."

Since the movie's release, Aitken has been pleased with the response both the scene and Thanos has received. "It was very satisfying seeing how many people reacted to him. People think he's great."

Yet he still has mixed feelings about the whole script business.

"I was allowed to read the script while the cast weren't -- I feel a bit bad about that."

Avengers: Infinity War is currently Hulk-smashing it in cinemas worldwide.

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