BIG Preview AND TRAILER: The Avengers Infinity War cast speak

Avengers: Infinity War is the film superhero fans have been waiting a very long time for.

Boasting 30 key cast members, its release marks the 10-year anniversary of the Marvel Cinematic Universe, which began with Iron Man.

While details of the plot are shrouded in secrecy, we know we'll see the Avengers and their allies trying to protect the world from Thanos, a dangerous menace who has emerged from the cosmic shadows.

And one other thing's for sure - it will be 156 minutes of adrenaline-fuelled action as the deadliest showdown yet plays out.

Here, some of the film's biggest stars tell us more.

Based on the Marvel comics first published in 1963, this is the third film in the Avengers franchise and the 19th Marvel Studio film to date.

So, why does Chris Pratt, who plays Peter Quill/Star-Lord, think the Marvel Cinematic Universe (MCU) has such staying power?

"You can have films that can be more irreverent and funny and space opera, you can have action thriller, you can have socially relevant Shakespearean drama, fantasy - various genres all fall under the MCU umbrella and somehow, tonally, are resonant and interchangeable, as we'll see in this film," the 38-year-old explains enthusiastically.

One of the founding members of the Avengers is Tony Stark/Iron Man, played by New Yorker Robert Downey Jr - and in Infinity War, we will see him face his most complex issues and challenges to date.

Discussing the success of the Marvel films, Downey, 53, suggests: "It's about creativity. We're talking about something that's really delicate and really needs to be nurtured, and it needs to be in the right environment or it will not flourish.

"This Marvel Cinematic Universe has enjoyed great weather. It has enjoyed great soil. And it's just crazy. It's like the harvest gets better year-by-year.

"And what I'm most excited about now is that I really do think, particularly in the next several years, that the best stuff is yet to come."

The last Marvel adventure to hit our cinema screens before this was Black Panther, which has become the highest-grossing superhero film at the domestic box office since its release earlier this year.

And Avengers: Infinity War incorporates Wakanda - the fictional African nation at the centre of Black Panther - as a safe place for the Avengers to develop new tech and armour.

"Part of what has been great about the way the Black Panther character, and Wakanda, has been handled is that he's not necessarily trying to fit into the Avengers," notes US star Chadwick Boseman, 40, who plays T'Challa (otherwise known as the Black Panther himself).

"In fact, the Avengers are coming into his world because he's made it known that it exists. It's a progressive way of thinking about it. He's not just another cog in the wheel."

Black Panther may have become both a financial success and a massive cultural phenomenon, but 24-year-old Letitia Wright, who plays Shuri, the younger sister of T'Challa, didn't expect to get the call about being part of the Avengers.

Of reprising her role, she enthuses: "We get to have fun, and put out entertaining movies, but throw subject matters in there that we can really think about as a society, and make us reflect on ourselves."

Another face people will be excited to see is that of Chris Hemsworth, who was absent for "Captain America: Civil War".

The 34-year-old plays the God of Thunder, Thor, and muses: "To have an opportunity to attack a character again and hopefully advance on that and bring something unique to it each time is a real challenge.

"But if you can pull it off, it's pretty creatively satisfying."

Indeed, for Pratt, playing a superhero is a "very rewarding job".

"The times I feel the very best in my soul is when I can use the fact I'm a superhero and I can go and I can cheer up some sick kids. I can show up in a young innocent kid's life, who may be terminally ill, I can help raise money for a great cause," says the Minnesota-born star.

"The opportunity to use the power that superheroes have over the imaginations of kids has been the most rewarding [thing] for me."

Zoe Saldana, the New Jersey-born actress responsible for the character of Gamora, also from the Guardians of the Galaxy franchise, echoes her co-star.

"A younger audience deserve entertainment, but they also deserve inspiration and strong messages of hope and dreams and a great sense of justice, and sometimes, what are considered high quality films for award seasons, overlook a younger audience," says the 39-year-old.

"So, I'm happy and honoured to fill in that space, and I take it with a lot of pride as a mother of three boys."

Of course, no superhero film is complete without a terrifying villain, and that role in Avengers: Infinity War falls on Josh Brolin, 50.

In the cosmos, the Infinity Stones are the most powerful items one can possess, and Brolin's character Thanos believes that if he can secure all six, he can bring balance to the universe.

It would also mean he could permanently kill 50% of life with a snap of his fingers.

"He's not a good guy, but his idea makes sense to him," says Brolin. "But then you have to ask the question, who is he doing it for? Is he doing it really to save the other half? And is that justifiable? You can really dig into that whole thing. It's really fun to bring all that out."

The film's story may be very much focused on Thanos, but Brolin insists he doesn't feel pressure as an actor.

"When you're doing it, you're not thinking about that," he explains. "You are in a bubble and you are on this trip and, to me, you get consumed by that."

However, he does admit experiencing the fandom around his character can be "unnerving".

"I'm not used to that," he says. "So, this is a new world for me.

"I enjoyed the process very much - the reaction, I don't know. But, we'll see."

Avengers: Infinity War is out now.