3. Natasha Romanoff / Black Widow
Natasha Romanoff made her MCU debut in Iron Man 2 but it was her significant role in The Avengers that really showcased what a force-to-be-reckoned with that she was. A SHIELD spy working for Nick Fury, she was tasked with bringing The Avengers together, but her expertise at getting the job done and efficiency in the field meant that she ended up becoming one of them.
Natasha was a character with conviction and a strong moral compass. Yes, she had committed a lot of unforgivable acts in the past and she was still capable of crossing lines for the greater good, but she always wanted a life where she could use her skills for good, and joining The Avengers gave her that opportunity.
From Scarlett Johannsson’s impeccable performance to Natasha’s all-around badassery, Black Widow was an exquisite part of the MCU and she was never fully given the exploration she deserved. She was the glue that held The Avengers together in their early days when they were bickering with each other, and again in a post-Blip world. And her ultimate sacrifice to save her best friend proved beyond a shadow of a doubt that this former assassin had become the one thing she always wanted to be: A hero.