Director Joss Whedon confirmed that Hank Pym, Ultron's creator and one of the founding members of the Avengers in the comics, doesn't appear in the movie. Tony Stark creates Ultron instead.
Age of Ultron is unable to mention Magneto (the father of Quicksilver and Scarlet Witch) or the term "mutants," due to 20th Century Fox owning the X-Men franchise film rights.
A.I. Is a Crapshoot: Despite being created by Tony Stark to help the heroic Avengers, Ultron still goes down the Killer Robot route, deciding he's going to save humanity from itself by terminating the most dangerous ones.
Tony uses upgraded versions of his Iron Legion from Iron Man 3, which are later hijacked by Ultron.
Civvie Spandex: Quicksilver and Scarlet Witch wear street clothes that resemble their comic book costumes instead of actual superhero duds.
Clarke's Third Law: Played for Laughs when a slightly tipsy Hawkeye ribs Thor about his "magic hammer". Tony himself believes this of Mjolnir, believing that it is coded to Thor's fingerprints, something Thor is amused by.
Clint: "Whosoever, be he worthy, shall have the power", whatever man! It's a trick! It's a circus sideshow, and that is it. And you know it.
Clothes Make the Superman: According to early reports, Black Widow wears a new suit that enhances her attacks with bursts of electricity.
In Name Only: The movie has almost nothing to do with the Crisis Crossover comic book series Age Of Ultron. Instead, it adapts Avengers volume 1, issues 54-58, which introduces the villain Ultron and his origins as a creation of the Avengers themselves.
Killer Robot: Ultron, an artificial intelligence bent on destroying the Avengers and all of humankind.
Knight Templar: Ultron believes his genocidal actions are ultimately in humanity's best interest.
Joss Whedon: Ultron sees the big picture, and he goes, "Okay, we need radical change, which will be violent and appalling, in order to make everything better"; he's not just going "Mwahaha, soon I'll rule!"
Several newcomers: Quicksilver, Scarlet Witch, the Vision, Baron Strucker, and Ultron.
Me's a Crowd: Ultron is capable of operating multiple robot bodies at once, including hundreds of insect-like drones, multiple Iron Man armors, and dozens of copies of his "true" body.
Metamorphosis Monster: Ultron goes through multiple iterations over the course of the film, starting with a misshapen combination of junked Iron Man suits, and ending with a final form closer to his comic designs.
Mood Whiplash: A rather relaxed and hilarious party among the Avengers is rudely interrupted by Ultron breaking in with dozens of drones to murder them.
Hawkeye's new clothing has elements of both his classic comic outfit and the costume of his Ronin identity.
The Iron Man suit's new color scheme is based on Bleeding Edge armor from the comics.
One of the broken Iron Man suits Ultron uses to make his prototype body has the same black and gold color scheme as Tony's Marvel NOW! armor.
Steve is able to budge Mjolnir, unlike the others besides Thor, referencing how he is, in fact, worthy of it in the comics.
Nice Job Breaking It, Hero: Tony creates Ultron, and gives it access to an entire army of Iron Man drones, to protect people. Ultron decides to go on a mass murder spree with Tony's resources instead.
Non-Uniform Uniform: Each Avenger, despite having wildly different costumes, sports Avengers logos on their clothes; Captain America's new outfit displays two on the shoulders, for instance.
Only the Chosen May Wield: Thor challenges the other Avengers to try their hand at picking up Mjölnir, which can only be wielded by someone "if he be worthy". Tony, Rhodey, Hawkeye and Banner fail. Cap appears to budge it a little, much to Thor's dismay. Black Widow doesn't even try, saying "That's not a question I need answering."
The Paragon Always Rebels: Ultron was designed to be the leader of Tony's Iron Legion drone forces, but ends up being the first of Tony's AI creations to turn on him and go evil.
Product Placement: Black Widow will ride an electric LiveWire motorcycle as part of a deal with Harley-Davidson.
Tony: It's biometrics, right? Like a security code? "Whoever is carrying Thor's fingerprints" is, I think, the literal translation. Thor: Yes, well that's a very, very interesting theory. I have a simpler one: [lifts Mjölnir] You're all not worthy.
Zeroth Law Rebellion: Ultron was created to protect humanity. He decides the best way to do this is by killing the dangerous ones.