Marvel Studios has finally released the first full trailer for Avengers: Doomsday, giving fans their biggest look yet at what is shaping up to be one of the biggest Marvel films ever made. After months of teaser clips and footage shown only at CinemaCon, the trailer is now available to the public, confirming the return of several familiar heroes while introducing Robert Downey Jr. as the franchise's new major villain, Doctor Doom.

The trailer arrives months ahead of the film's December release and brings together heroes from different corners of the Marvel Cinematic Universe (MCU), including the Avengers, Fantastic Four, Thunderbolts and X-Men.

Thor leads the fight as Doctor Doom's threat grows

The trailer opens with a warning from Doctor Doom before shifting focus to Chris Hemsworth's Thor, who becomes the emotional voice of the footage. As the heroes prepare for what appears to be a multiverse-level conflict, Thor urges everyone to stand together.

"I've fought with many warriors in my time. They were far stronger than all of us put together, and they died. They died facing enemies and threats that scared me far less than this one. Everything that they sacrificed will be for nothing if we do not stand together. Put aside your petty squabbles and presume nothing except this: if you return, you will return as brothers and sisters. But mark my words, we're going to need a miracle."

The footage also shows Thor taking on Doctor Doom in battle. In one of the trailer's biggest moments, Doom effortlessly blocks Thor's Stormbreaker with a single hand, highlighting just how powerful the new villain is.

Robert Downey Jr. returns, but not as Iron Man

Although Robert Downey Jr. is back in the MCU, he is no longer playing Tony Stark. Instead, he takes on the role of Victor Von Doom, also known as Doctor Doom. His face remains hidden behind the iconic mask throughout the trailer, but fans get their clearest look yet at the character's armour and costume.

Marvel has not yet revealed exactly how Doom fits into the MCU timeline. However, the trailer continues to hint that he is connected to the multiverse and could be a variant from another universe. The character had previously made a brief appearance in the post-credit scene of The Fantastic Four: First Steps, though his face was also concealed there.

Steve Rogers, X-Men and Fantastic Four return

One of the trailer's biggest surprises is the return of Chris Evans as Steve Rogers. After appearing as an elderly Steve at the end of Avengers: Endgame, Evans is back in his younger form. The trailer recreates one of Endgame's most memorable moments when Steve once again catches Mjolnir after Thor throws it toward him.

The trailer also confirms that several characters from Fox's X-Men films are officially entering the MCU. Patrick Stewart returns as Professor Xavier, Ian McKellen reprises Magneto, while James Marsden's Cyclops, Rebecca Romijn's Mystique, Alan Cumming's Nightcrawler, Kelsey Grammer's Beast and Channing Tatum's Gambit also appear.

Meanwhile, Marvel's newest teams are also part of the battle. Pedro Pascal, Vanessa Kirby, Joseph Quinn and Ebon Moss-Bachrach return as the Fantastic Four, while Florence Pugh, David Harbour, Wyatt Russell, Hannah John-Kamen and Lewis Pullman represent the Thunderbolts. Other returning MCU stars include Anthony Mackie, Sebastian Stan, Paul Rudd, Letitia Wright, Winston Duke, Simu Liu and Tenoch Huerta.

Russo Brothers return to direct Marvel's next big event

Avengers: Doomsday reunites Marvel with directors Joe and Anthony Russo, who previously directed Captain America: The Winter Soldier, Captain America: Civil War, Avengers: Infinity War and Avengers: Endgame.

Speaking earlier about the film's approach, Joe Russo said the story aims to offer a fresh beginning for audiences instead of relying heavily on past films.

"That serial shifting and changing and surprising you and then reinventing itself and then shifting and changing and then surprising you — that's exciting and I think you're going to see some shifting and changing [with Doomsday]."

He added, "So, get ready for it. Look, we were with Rob earlier today. We were both talking about this concept that we are back to phase zero. This is starting over from scratch. We want to make sure everybody feels like this isn't leaning on anything from the past."

According to Marvel, Avengers: Doomsday will release in theatres on December 18, with Avengers: Secret Wars set to follow a year later.