Black Widow is a marvel super hero who is built around structure. Looking into the marvel cinematic universe we learn about Black Widows origin were she was trained to be an assassin as a young girl in Russia. From her time there Black Widow, or as others call her Natasha Romanoff, was trained to kill anyone in the most efficient way possible. It is for that reason that she is sterilized at a young age to help in her efficiency. All of her train made Black Widow the great assassin that she is, even if it mentally scared her for the rest of her life. The strict training along side the many missions she was given as an assassin made her well known in the world of esnpianash. Because she was so renowned S.H.I.E.L.D. sent Hawkeye to kill her, but instead of killing her she was offered a place at S.H.I.E.L.D. as an agent. Black Widow would go from one structure to another when joining S.H.I.E.L.D. and then eventually joining the Avengers. Even as an Avenger who has more freedom from structure it is because she was hammered with it at a young age Black Widow still follows certain protocols when a situation arrises. Due to her past Black Widow was not always a hero but through her growth as a character she was able to become more then just a hero but an Avenger, and people can argue that her past made her a horrible person for a time I believe it was a necessary process she had to go through in order to do the right thing in the end and help people for the greater good. That is what make Black Widow heroic if not more. Black Widow is an Avenger that will use her skills to serve and protect the ones around her. Even if she was not always good that does not change the fact that she is heroic now.