This one requires some reading between the lines so bear with me.
Joss Whedon publicly debunked the notion that Hank Pym would be the creator of Ultron in the cinematic universe as he is in the comics. But just because we don't see Pym create Ultron in the Avengers, doesn't mean he still didn't have something to do with it. As we know, Marvel loves weaving threads of interconnectivity via cleverly placed easter eggs (Think Captain America's shield in Iron Man 2 or the Stark Expo in Captain America). If we take recent Ant-Man casting news, throw in a dash of plot rumors, sprinkle that with the official Age of Ultron synopsis and mix it all together, we have a solid theory that may blow some fanboy minds. Let's take a look:
- John Slattery is reprising his role as an elder Howard Stark in Ant-Man
- He will presumably appear in flashback sequences with a young Hank Pym as both were tech-savy inventors ahead of their time
- The opening line of the official synopsis for Age Of Ultron reads: "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."
It sounds to me like Tony Stark will stumble onto the work of his father and Hank Pym (not unlike how he used his father's work to synthesize a new element in Iron Man 2) and breathe new life into the aforementioned "dormant peacekeeping program," only to have it all go wrong resulting in the creation of Ultron. It would be a great way to offer a unique twist on Ultron's origin that fits with the direction the MCU has been taking thematically (reliance on A.I. and machines in Iron Man 3 and a distrust of traditional authority in The Winter Soldier) while still remaining loyal to his comic book roots. Also, seeing even a passing reference to Ultron in an Ant-Man flashback would be a great way to tie things together, since Ant-Man will be the first film out of the gate after Age Of Ultron.
I'm sure I'm not the only one who's thought about this but I would love to hear alternate theories or ideas. Sound off in the comments!