The follow-up to the 2012 blockbuster has been referred to up until now as "Avengers 2," but Whedon introduced a short CG animated video that revealed the film's official title: "Avengers: Age of Ultron."
"Age of Ultron" is the title of a recent mini-series written by Brian Michael Bendis that found the Marvel Universe effectively destroyed by The Avengers' longtime nemesis Ultron. In the comic books, Ultron is an artificial intelligence accidentally created by Avenger Henry Pym (Ant-Man) for the greater good. Instead, Ultron - in robotic form - decides all of humanity must be destroyed beginning with his "father."
The Avengers and other Marvel heroes have foiled Ultron time and time again, but have never been able to completely destroy him. There is always a piece of his programming somewhere repopulating and strategizing. In "Age of Ultron," Avenger Wolverine found himself going back in time to kill Pym before he created Ultron in order to save the world. This ends up affecting the time stream and changing history. Eventually order was restored, but there are long-term consequences that are currently playing out because of the event in different Marvel titles.
Because of the complexity of the Ultron mythology and multiple backstories (not to mention the involvement of Wolverine, a character Marvel Studios currently does not have the rights to use on the big screen), this would be an unlikely backdrop for the movie's storyline. It is possible, however, that certain elements from the event will inspire Whedon's screenplay.
What the title and the recognizable Ultron head that accompanied it does mean is that Thanos will not be the villain in the next movie. The Death God from Titan briefly appeared at the end credits of "The Avengers" as the behind-the-scenes conspirator to power Loki's alien invasion, but he'll likely be back to quarrel with Earth's Mightiest Heroes down the road.
"Avengers: Age of Ultron" is scheduled to open nationwide May 1, 2015.