This week Marvel Studios is releasing Captain America: The First Avenger, a period superhero adventure starring one of their most recognizable characters. But it's also a prelude to the company's next feature, which will be a kind of comic-book movie that hasn't been attempted on the big-screen before: a team-up adventure that unites some of Marvel's biggest heroes -- including Iron Man (Robert Downey Jr.), Thor (Chris Hemsworth), Captain America (Chris Evans) and The Incredible Hulk (Mark Ruffalo, taking over from Ed Norton and Eric Bana) -- to combat a global threat. The title, of course, is The Avengers, the same name of the Marvel supergroup that's been battling bad guys in the four-color pages of the company's comics since 1963. Geek icon (and part-time comics scribe) Joss Whedon is writing and directing the film, which also stars Samuel L. Jackson as the group's leader, Nick Fury, Scarlett Johansson as the leather-jumpsuit clad spy, the Black Widow and Jeremy Renner as the ace archer, Hawkeye. Naturally, a project as ambitious as The Avengers didn't come together overnight. Marvel has been laying the groundwork for this film since the first Iron Man hit theaters in 2008, slipping in visual and verbal references to Avengers-lore in all their standalone superhero features. Here's a film-by-film guide to some of the Easter Eggs that have pointed the way to The Avengers