Note: This post contains spoilers of Avengers 2: Age of Ultron.
I liked Avengers 2: Age of Ultron, but as tends to happen with Marvel villains, Ultron's motivation is unclear. Why does he interpret his mission of "peace in our time" as "kill everyone"? Why does he hate Tony Stark so much? I have two ideas about this.
The first idea is that Tony didn't actually create Ultron. He simply downloaded the consciousness of the mind stone into a computer. As evidence of this, when Ultron is first activated, one of the first things he asks Jarvis is "Where is your body?", and upon learning that he's a machine, says "This feels weird. This feels wrong.".
Under this interpretation, the reason he hates Tony so much is because Tony is the one who put him into a machine. He hates Tony more than Bruce Banner, because it was Tony's idea. As for the mission, he never cared about peace. He just said that to confuse and make fun of the Avengers.
The second idea is that Tony did actually create Ultron, and Ultron was performing his mission. He saw that humans are a divisive and warlike species. He realized that we would never accept an externally imposed order. But that we might unite to fight a common enemy. And that plan worked, at least as far as getting the Maximoffs to put aside their differences with the rest of the Avengers.
In this case Ultron hating Tony was the lie. Ultron figured that Tony, having created him, would be less willing to fight him. So he made sure Tony would think he he hated him, so Tony would hate him back.