They may not be as instantly recognisable as The Hulk or Iron Man, but this ragtag team of misfit superheroes that patrol the outer reaches of the Marvel universe are just as colourful. A bickering bunch of cosmic space freaks, they headline what is undoubtedly the weirdest-looking Marvel film yet.

It certainly confused some of its stars. "I was like, 'Guardians? There's a person, that's a tree and there's a raccoon'," says Zoe Saldana. She's referring to Rocket Raccoon (voiced by Bradley Cooper) and Groot (voiced by Vin Diesel) - two computer-animated characters that make up two-fifths of the Guardians, alongside Saldana's green-skinned humanoid Gamora, a monosyllabic, tattoo-clad brute named Drax The Destroyer (Dave Bautista) and Peter Quill (Chris Pratt), a human-born pilot also known as Star Lord.

Orbiting this quintet is a wealth of characters set to expand Marvel's dramatis personae - from Del Toro's The Collector to Ronan the Accuser (Lee Pace), a villain said to be in league with Thanos (voiced by Josh Brolin), to members of the Nova Corps, the intergalactic police force that patrols the galaxy, led by John C. Reilly's Rhomann Dey.

It's a wild cast. Just ask Djimon Hounsou, the Benin-born star of , who plays Korath the Pursuer.

"I'm sort of a bad guy," he says. "I play a humanoid, a machine that looks like a man. I'm created just to pursue. Like a Terminator."

Hounsou was another cast member who knew little about the franchise. "The character I'm playing has not been well-developed yet in the comic world."

In some ways, it's as if the creators are starting on a blank canvas. "It's a real change in direction for Marvel, in my opinion," says Scottish-born Karen Gillan, who plays a villainess in . "Just the tone of it - it's really funny and has a cool soundtrack."

The question is, will it be too many new characters and elements unfamiliar to audiences? Already, Marvel and parent company Disney have been working overtime - even launching a website called Galaxy Getaways, an online travel agency designed to introduce us to alien destinations featured in the film.

The 36-year-old Saldana, who has already put her stamp on two huge sci-fi franchises, in J.J. Abrams' reboot and James Cameron's , could arguably have used such a guide when it came to the Guardians or their opponents. "Apparently, they fight with the Avengers. I didn't even know who the Avengers were," she says, shrugging. Needless to say, she's done her homework since, no doubt discovering that in Guardians folklore, her character Gamora was once adopted by the evil Thanos.

Saldana's reasons for coming on board were rather more down-to-earth.

"I loved the script when I read it," she says. "And I like James Gunn. He's my kind of director - animated, passionate, alive, young, fresh, full of ideas, willing to give 150 per cent. I like the array of actors that he put together for the movie."

A 43-year-old from Missouri, Gunn seems an ideal choice to direct, given his last feature movie was - the 2010 comedy about an ordinary guy who turns himself into a superhero called the Crimson Bolt.

Indeed, Gunn's casting choices are to be applauded for the daring selection of up-and-coming actors rather than A-list stars. Take the aforementioned Karen Gillan: well-known in Britain for her role in sci-fi TV show , the 26-year-old actress is barely known internationally, but Gunn cast her as a blue-skinned villainess in league with Ronan the Accuser.

"It was a really cool transition for me," she says. "My dad has always said 'You don't want to play a Bond girl. You want to play a villain.' Basically, don't just settle for running around in dresses."

One of the film's centrepiece moments promises to be the showdown between the now-opposing Gamora and Nebula, who were once trained to be killers, in the service of Thanos.

"It's a big epic fight sequence," says Gillan. "It was amazing but it was really demanding, because we had to be able to do everything. I had to train every day that I wasn't shooting on the film. I had to learn the fight sequence and learn basic stuff like kicking and punching, and form and just how to hold yourself; everything, really."

For Saldana, who played a high-kicking assassin in 2011's , these scenes were easy. Much harder for her was enduring the make-up; after playing the blue-skinned Neytiri in , going green for Gamora was "challenging". Four to five hours in the make-up room, followed by constant tweaking - which drove her mad.

"It keeps moving, it keeps shifting, because the skin is an organ that will perspire, that will breathe, that will do this, that will crack, that will be dry."

She wasn't the only one to suffer for her art. Gillan had to chop her distinctive red locks off. Was it traumatic? She shakes her head. "I just sat in a chair and they started shaving it off my head, and then I fell asleep for two hours."

Unveiling her new look at last year's Comic-Con in San Diego, when she whipped off a wig, was the perfect way to announce herself as one of Marvel's new It girls.

Upping the female contingent has clearly been designed to widen audience appeal as much as possible, doubtless all part of Marvel's elaborate master plan. Currently, Whedon's hugely anticipated sequel, , is being readied for a May 2015 release, concluding Phase 2. Though not said to feature any of the cast, fans are already speculating that both sets of characters will collide, against Thanos, in one almighty third film. Will it? Only time - and those end credits - will tell.

opens on July 31