Despite starting off as a supervillain, Black Widow is now regarded as one of Marvel's top superheroes and was even a founding member of the movie version of the Avengers.
As the years have gone by, we've learned more and more about the Russian super-spy's murky past, including her time training as an assassin in the mysterious Red Room.
However, it isn't just in-story that Black Widow has a dark past she would rather be forgotten. Along with the usual gamut of weird comic storylines and completely abandoned plot points (including an embarassing early defeat, an impossible family tree and a very surprising change of career), Natasha has also been at the centre of a huge amount of controversy regarding the alleged sexist treatment of the character in the movies.
Regardless of your views on the matter, it's certainly something Marvel would rather people just stopped talking about.
Marvel have done plenty of things with the character that they would rather just be forgotten about and hidden away from prying eyes. Just like a well-trained secret agent though, we're going to sneak into the Marvel Vaults and spill the beans on all the dirty little secrets they've been trying to hide.