The first Avengers: Age of Ultron trailer for writer/director Joss Whedon’s highly anticipated superhero follow-up has leaked online under a week before its official release.  The sequel finds Iron Man (Robert Downey Jr.), Captain America (Chris Evans), Black Widow (Scarlett Johansson), Thor (Chris Hemsworth), Hulk (Mark Ruffalo), and Hawkeye (Jeremy Renner) teaming up once again to battle the devious robot known as Ultron (James Spader).  This is very close to the footage that was shown at Comic-Con, save for a different final shot and an extended clip that was shown of the so-called "Avengers Party."  What's clear from this trailer is that the tone is darker, the stakes are higher, and the threat is seemingly more nefarious.

Watch the trailer after the jump.  Avengers: Age of Ultron also stars Elizabeth Olsen, Aaron Taylor-JohnsonPaul Bettany, Don Cheadle, Andy Serkis, and Samuel L. Jackson and opens in theaters May 1, 2015. 

Here’s the official synopsis for Avengers: Age of Ultron:

Marvel Studios presents “Avengers: Age of Ultron,” the epic follow-up to the biggest Super Hero movie of all time. When Tony Stark tries to jumpstart a dormant peacekeeping program, things go awry and Earth’s Mightiest Heroes, including Iron Man, Captain America, Thor, The Incredible Hulk, Black Widow and Hawkeye, are put to the ultimate test as the fate of the planet hangs in the balance. As the villainous Ultron emerges, it is up to The Avengers to stop him from enacting his terrible plans, and soon uneasy alliances and unexpected action pave the way for an epic and unique global adventure.

Marvel’s “Avengers: Age of Ultron” stars Robert Downey Jr., who returns as Iron Man, along with Chris Evans as Captain America, Chris Hemsworth as Thor and Mark Ruffalo as The Hulk.  Together with Scarlett Johansson as Black Widow and Jeremy Renner as Hawkeye, and with the additional support of Samuel L. Jackson as Nick Fury and Cobie Smulders as Agent Maria Hill, the team must reassemble to defeat James Spader as Ultron, a terrifying technological villain hell-bent on human extinction. Along the way, they confront two mysterious and powerful newcomers, Wanda Maximoff, played by Elizabeth Olsen, and Pietro Maximoff, played by Aaron Taylor-Johnson, and meet an old friend in a new form when Paul Bettany becomes Vision.

Written and directed by Joss Whedon and produced by Kevin Feige, Marvel’s “Avengers: Age of Ultron” is based on the ever-popular Marvel comic book series “The Avengers,” first published in 1963. Louis D’Esposito, Alan Fine, Victoria Alonso, Jeremy Latcham, Patricia Whitcher, Stan Lee and Jon Favreau serve as executive producers. Get set for an action-packed thrill ride when The Avengers return in Marvel’s “Avengers: Age of Ultron” on May 1, 2015.

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Image via Marvel