Another Cap 2 inspired thread, if anyone felt inspired to read some comics after seeing the movie!
Natasha Romanoff/Natalia Romanova aka Black Widow is a former KGB agent, one of S.H.I.E.L.D's best agents and a member of various Avengers teams along the line.
Natasha was born circa 1928 and was trained from a very young age in the Russian government's "Red Room" facility to become a highly efficient spy and assassin. She also underwent some physically enhancements that slowed her aging, so that she's still young in the present despite being one of the oldest Avengers. (Her background in the movies hasn't really been explored, so I have no idea if this applies there or not)
She made her first comic appearance in 1964 as a Soviet spy and enemy of Iron Man.
Ok, Black Widow's comic history isn't really that straightforward as far as I can tell and I haven't read that much stuff with her yet. A couple of things I would really really recommend though are
Black Widow: Name of the Rose (2010) and the currently ongoing
Black Widow (2014) with great art by
Phil Noto.
Since I'm not that informative,
this seems to be a pretty comprehensive list of stuff she's been in if you're looking for more!