"Ultron-5" is the twenty-second episode of The Avengers: Earth's Mightiest Heroes.
The Avengers face the Serpent Society, who have taken hostages. King Cobra claims they are working for Viper, but it cannot be as she was recently locked up. Giant-Man tries to reason with the villains, but his attempts at diplomacy only manage to endanger the Avengers and the hostages. The battle ends with Hawkeye injured and massive property damage.
Hank decides he cannot recoincile his pacifist nature with the Avengers' violent ways and resigns the team, which upsets Wasp. Black Panther and Hulk bring the recently defeated Red Ghost, who tried to attack the Fantastic Four using plans and codes given by an anonymous source. It turns out that both the orders of "Viper" and the message to the Red Ghost came from Avengers Mansion. The culprit reveals himself as Pym's robot Ultron, who knocks Hank out, captures Wasp and takes control of Iron Man's armor and the Quinjet with Hulk inside it. He also takes control of the training room, whose machines attack Captain America, Hawkeye and Jane Foster, who had come to tend Hawkeye's injuries.
Ultron tells the captured Wasp he has reasoned that humanity is flawed, so he must eliminate all humans so the world can achieve true peace and order. The Avengers get the upper hand on the Ultron-controlled machines and go to face the killer robot, who seemingly disintegrates Thor with a single blast. Wasp frees herself by revealing she can also grow in size and Hulk escapes the haywire Quinjet, then smashing Ultron into pieces.
Uberknownst to anyone, the Enchantress teleported Thor at the moment of the blast and is keeping him hidden in her personal paradise just for the two of them to be together.
Hank destroys all remains of Ultron technology, but doesn't notice the still glowing eyes of the robot's head...
- Besides the Serpent Society and Red Ghost, Ultron reveals he also manipulated Radioactive Man to attack the arc reactor in The Casket of Ancient Winters.