Robert Downey Jr. returns to Marvel as Doctor Doom

Robert Downey Jr. stunned fans as he removed a mask during Saturday's San Diego Comic-Con Hall H panel, revealing that the "Iron Man" actor will rejoin the franchise as one of Marvel's biggest villains named Doctor Doom.

The panel was flooded with hooded figures concealed by masks that resembled the iconic comic book villain known for his skills in both sorcery and science when Downey Jr. revealed himself.

"I like playing complicated characters," he said as fans began to chant his name.

The Russo Brothers, who are returning to direct both Avengers: Doomsday and Avengers: Secret Wars, believe that while Downey Jr. has a "new mask," he, the rest of the Marvel team, and everyone else has the "same task" of helping to "create the greatest possible experience" at the movie theatre.

Another major villain joining the Marvel Cinematic Universe is cosmic entity called Galactus, which will be the antagonist of The Fantastic Four: First Steps, and directed by WandaVision director Matt Shakman.

The panel had plenty more show-stopping moments, as it began with a boisterous Deadpool choir, inspired by the recent film Deadpool and Wolverine, which Marvel president Kevin Feige said set the box office record for the highest grossing R-rated film ever on Saturday.

Different iterations of the silly red-costumed character named Deadpool danced around the Hall H floor, walking amidst the seated attendees as the film's anthem Like a Prayer by Madonna played.

Deadpool & Wolverine has the largest domestic box office opening of 2024, according to industry analysts. US and Canadian sales through Sunday should hit between $175 million and $185 million, said Paul Dergarabedian, senior media analyst at Comscore.

The cast of the upcoming film Captain America: Brave New World, later joined the stage with lead Anthony Mackie sharing how his version of the titular superhero is different from actor Chris Evans' version.

"Sam is surrounded by a host of intricate characters that help him move through the plot of the story. He's not so much a muscle bound guy, he's more of a cerebral, thoughtful character," Mackie said.

Following that Indiana Jones actor Harrison Ford, who replaces William Hurt's role as antagonist 'Thunderbolt' Ross, joined the cast and playfully "hulked out" with his arms out and mouth open and then chases Mackie around the stage

"It's been like this for a long time," Ford said, adding that he's proud to become a member of the Marvel universe.

David Harbour later walked into Hall H amidst the seated audience members wearing the costume for his Black Widow character named Alexei Shostakov.

He approached the stage to address the other cast members of the Thunderbolts, which centres on a team of Marvel anti-heroes, with a monologue complaining about them ignoring his idea for them all to dress up for the film.