SAN DIEGO, July 26 - In one of Comic Con's most awaited presentations, Marvel superheroes of all kinds from Iron Man to Ant-Man took over the fan convention on Saturday, as leading actors revealed surprises to films that will showcase the characters. "Avengers: Age of Ultron," the highly anticipated sequel to 2012's superhero ensemble "Avengers," brought out a star-studded panel that included Robert Downey Jr (Iron Man), Chris Hemsworth (Thor), Chris Evans (Captain America) and Samuel L. Jackson (Nick Fury). "This is the longest bench of talent I've ever been on," Downey said. "I become a little less significant every time and that's fine because they're all just that damn good." In 2012, "Avengers" became the fastest film to cross the $1 billion milestone at the global box office. The sequel introduces Aaron Taylor-Johnson as Quicksilver, Elizabeth Olsen as the Scarlet Witch and Paul Bettany as The Vision. James Spader will play villain Ultron. Comic Con, an annual convention in San Diego that began as a gathering of comic book fans and a home to creative content for fringe and cult audiences, has become a top venue for movie studios to unveil blockbuster projects. The audience at the Marvel showcase was shown a sneak peek that begins with the group of superheroes joking over drinks. The banter quickly turns to action-filled drama as the superheroes have to reunite to save people from Ultron. Olsen, one of the two women on the panel for the film, said her character's use of magic "ends up adding something epic to the fights, it's a new element." Spader said he enjoyed his turn as the villainous 8-foot (2.4-metre) tall robot Ultron, describing the experience as "startling and surprising and challenging and exciting." Walt Disney-owned Marvel Studios has become a dominant force at the box office with superhero films franchises such as "Iron Man," "Captain America" and "Thor." Mavel is releasing "Guardians of the Galaxy," about a rogue group of galactic heroes on Friday and the film is already drawing strong reviews from critics and word-of-mouth with fans. "Guardians of the Galaxy 2" was announced on Saturday's panel as scheduled for release on July 28, 2017, and James Brolin was revealed to be super villain Thanos, entering the stage wearing Thanos' Infinity Gauntlet. Also presented was a first look at new film "Ant-Man." The hero is the alter-ego of electronics expert and sometime burglar Scott Lang, portrayed by Paul Rudd, who has the ability to shrink to the size of an insect. Michael Douglas will play scientist Dr Henry Pym, who invents the ability for humans to change size, Corey Stoll will play villain Darren Cross, who was revealed to be Yellowjacket, and Evangeline Lilly was revealed to be Hope Van Dyne, daughter of Hank Pym. Fans were treated to a clip showing Rudd as Ant-Man, shrunk to the size of an insect and escaping on the back of a fly.