The Avengers (known as Avengers Assemble in the UK and Ireland) is a 2012 Live-Action Adaptation of The Avengers comic book directed by Joss Whedon and produced by Marvel Studios and is the sixth film in the Marvel Cinematic Universe.
The story revolves around the heroes of the first five Marvel Cinematic Universe films (Iron Man, The Incredible Hulk, Iron Man 2, Thor, and Captain America: The First Avenger) banding together to form the eponymous super team as they tie up several unresolved plot threads from those movies.
Warning: Unmarked spoilers for the previous films below.
Following the end of Captain America: The First Avenger, S.H.I.E.L.D. has recovered the Tesseract, an Asgardian relic they hope can serve as a source of infinite energy. However, their experiments with the device attract the attentions of Loki, the Big Bad of Thor, who promises the Tesseract to a third party in exchange for an army to conquer the Earth.
To stop Loki, S.H.I.E.L.D. director Nick Fury assembles super soldier living legend Steve Rogers (Captain America), billionaire power armor aficionado Tony Stark (Iron Man), Loki's physical god brother Thor, occasional enormous green rage monster Bruce Banner (The Hulk), and master assassins Natasha Romanoff (Black Widow) and Clint Barton (Hawkeye). Now the six heroes must set aside their conflicting personalities and motivations and work together if they hope to save the world.
An eight-issue prequel comic, The Avengers Prelude: Fury's Big Week has also been released, tying up loose ends from all the previous movies and setting the stage for this one. A second prequel mini-series focusing on Black Widow's activities leading up to the movie was also released.
Sequels include the 2015 Avengers: Age of Ultron and 2018 Avengers: Infinity War. If you're looking for the 1998 film based on the British TV series The Avengers, that's over at The Avengers. Don't worry, we won't tell.