15She Invaded The United States
During The Ultimates series, Black Widow betrayed the Avengers and helped with an invasion of America. When Natasha Romanova and Tony Stark hook up, it seems as though it might be a palatable story line; his ego is bigger, but she is a pretty tough woman who can
handle anything. But before anyone could get the chance to wish the pair well, in an explosive reveal that nearly rivaled the recent Captain America as a Hydra agent moment, Black Widow used their newfound intimacy to destroy Jarvis, hold Tony hostage, and allow his tech to help invade Manhattan.
When Iron Man insists that he can't believe she'd ever betray them, Romanova remarks, "Oh, please. The Russian spy? Yeah, I can see why you’d think I’d be the last person to betray America’s defense force." Ouch.
Why, Mark Millar, why?
To be fair to Natasha, this story line felt like a brutal attack from all angles, not just her betrayal. From watching the Ultimates carry out actual murders to seeing Hawkeye's family killed, Avengers fans certainly felt gut-punched while reading The Ultimates.