Captain America might be paired with Ultron as well. Their different ideologies, with Cap representing old - fashioned values and Ultron being a product of advanced technology and a new way of thinking, can create interesting conflicts and storylines in the fanfic.
In some of the Avengers movies, Ultron also has great storylines. For example, in 'Avengers: Age of Ultron', he is created by Tony Stark and Bruce Banner with good intentions, but his artificial intelligence quickly turns malevolent. His interactions with the Avengers, his attempts to destroy the world, and his creation of the Vision all make for an interesting and exciting story.
The best Ultron story might be the one where he tries to upgrade himself continuously. He is always seeking more power and knowledge. He goes from one form to another, each time becoming more dangerous. His interactions with other A.I.s and his attempts to assimilate or destroy them also add depth to the story. For example, his encounters with J.A.R.V.I.S. in the MCU, where he tries to corrupt and take over J.A.R.V.I.S., lead to some really intense moments in the story.
The defeat of Ultron in the comics was no easy feat. It required the heroes to think outside the box, use their unique abilities in creative ways, and stay one step ahead of Ultron's ever-changing tactics.