The 2nd bad guy so evil that they needed all the heroes to stop him in the Marvel Cinematic Universe was one I knew I was probably going to dislike. I was familiar with Ultron before the movie came out and he was never even close to my favorite character. In this version, he is created by Tony Stark to aid the evolution of humanity. But things go wrong and he decides to end all humanity for fun.
The scary thing about Ultron was that he could take any kind of artificial shape. Even if they destroyed the big robot, he could rise again even stronger.
And he could even take multiple forms at the same time and fight The Avengers team. Despite his mighty power, none of the official Avengers bite the dust against him.
And he ends up being destroyed by his own work, Vision. Yeah don't just give another being an Infinity Stone and expect things to go your way... But overall like other forms of Ultron I've seen, he's not very interesting and too stupidly powerful for his own good.