Carol Danvers has been around the Marvel Universe for decades; she actually debuted back in 1968 in the pages of Marvel Super Heroes #13. Working as a United States Air Force officer, she'd always been in contact with Mar-Vell, initially while he was using alter egos. In 1977, the revolutionary Ms. Marvel comic book series revamped her career. In this version, Danvers actually became a human-Kree hybrid, after being exposed to massive amounts of energy during an explosion that melded her genes with Mar-Vell's, effectively making her superhuman. The Ms. Marvel series was seen as a purposefully feminist comic book, which found Danvers fighting for equal pay when she was not superheroing; series writer Gerry Conway wrote that in Carol "you might see a parallel between her quest for identity, and the modern woman's quest for raised consciousness, for self-liberation, for identity."
For the next few decades, Ms. Marvel was a staple character in the Marvel Universe, but it wasn't until July of 2012 that Danvers officially assumed the position of Captain Marvel. Very quickly, Danvers not only became an Avenger, but she was also put in charge of S.W.O.R.D., an agency whos job is to protect the Earth from alien foes.