5. He created Ultron (in the MCU)
In the MCU, Ultron’s backstory was slightly altered. Instead of Hank Pym, Tony, along with Bruce Banner, was the creator of Ultron, which suited his way of dealing with problems quite well. Ultron was meant to be the ultimate weapon against threats to Earth.
Tragically, Ultron concluded that the entire human race should be exterminated. He attempted to do so but was stopped by the Avengers. In the related events, Quicksilver died.
Although Tony showed this from a fundamentally positive motivation, it is also a pretty arrogant thought to expect one can solve such problems in advance.
