Iron Man’s creation of Ultron inAvengers: Age of Ultron played a key role in the MCU, but one theory suggests that the true creator was actually Thanos. While Thanos’ most memorable appearances were in the final two Avengers movies, he makes several smaller onscreen appearances before that. Before he is even shown on screen for the first time, events happened that were retroactively revealed to have been instigated by the Mad Titan.
After the invasion of the Chitauri in The Avengers, Iron Man
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