With Marvel Studios reportedly closing in on an actress to portray Captain Marvel in future Marvel films and Carol Danvers playing a critical role in the currently unfolding "Civil War II" event, now's a great time to revisit -- or discover for the first time -- who, exactly, Captain Marvel is and what her legacy at Marvel Comics looks like.
The history of Captain Marvel began with 1967's "Marvel Super-Heroes" #12 (by Stan Lee, Gene Colan and Frank Giacoia), with one of the strangest set-ups for a Marvel superhero yet. Captain Mar-Vell was sent by the Kree military to Earth to investigate the planet and determine whether the Kree needed to dedicate themselves to destroy the planet (after the Earth heroes, the Fantastic Four, had drawn attention to the planet by defeating a few other Kree emissaries). Mar-Vell's commanding officer, Colonel Yon-Rogg (who was in love with Mar-Vell's girlfriend), wanted Mar-Vell dead, so he tried to sabotage Mar-Vell's mission.
In the next issue (with Roy Thomas now writing the series), Yon-Rogg tried to kill Mar-Vell but instead accidentally killed a human scientist, Walter Lawson, who was on his way to a restricted military base. Mar-Vell took on Lawson's identity and when he showed up at the base he met its head of security, a young woman named Carol Danvers, who was immediately suspicious of him. Yon-Rogg then tried to activate an old Kree sentry robot and have it kill everyone there, including Mar-Vell. Mar-Vell switches to his Kree battle uniform and saved their all of their lives. In all the confusion, they believed him to be a superhero called "Captain Marvel." That was the book's status quo for the first year of its existence -- Mar-Vell was spying on Earth, but while there he also ended up protecting the planet, while Carol Danvers investigated Lawson and Yon-Rogg kept trying to sabotage Mar-Vell's mission.
Eventually, Roy Thomas and Gil Kane decided to revamp the character. The initial set-up was supplied in "Captain Marvel" #16 (by Archie Goodwin, Don Heck and Syd Shores), where Mar-Vell helped stop a plot by Yon-Rogg and some other Kree higher-ups to overthrow the Kree's Supreme Intelligence. Yon-Rogg escaped to Earth and Mar-Vell convinced the Supreme Intelligence to let him take Yon-Rogg down (the Supreme Intelligence's first plan was just to blow up the Earth to get to Yon-Rogg). The Supreme Intelligence agreed, but gave Mar-Vell a new costume, special nega bands and a lock at the rank of "Captain." On the way to Earth, though, Mar-Vell got stuck in the Negative Zone. In the next issue (by Roy Thomas, Gil Kane and Dan Adkins), a new status quo debuted when Rick Jones discovered his own nega bands, and Jones can then switch places with Mar-Vell in the Negative Zone by clanging his nega bands together. This was, in effect, Roy Thomas' sly way of tying in the concept of the original Fawcett Comics Captain Marvel (where a young boy named Billy Batson shouts the name "Shazam!" to transform into Captain Marvel), as just like Billy Batson, Rick Jones disappears when Captain Marvel is drawn out of the Negative Zone. Mar-Vell now has the chance to track down Yon-Rogg to have their final confrontation, which takes place in "Captain Marvel" #18 (by Roy Thomas, Gil Kane, John Buscema and Dan Adkins) which also turns out to be a major moment in Carol Danvers' history.
Yon-Rogg uncovered a powerful piece of Kree machinery known as the Psyche-Magnitron and sought to use it to take control of the Kree Empire. Carol Danvers' investigation in the area ended when she was taken prisoner by Yon-Rogg. Mar-Vell then arrived to battle Yon-Rogg (and the powerful Mandroid, created by the Psyche-Magnitron). Eventually, Yon-Rogg tried to use his blaster on Mar-Vell, but accidentally shot Carol Danvers in her shoulder instead. This spurred Mar-Vell on to defeat Yon-Rogg. The only problem is that the Magnitron has now become unstable. Mar-Vell grabbed Carol and shielded her with his body as they escaped the explosion of the Magnitron, an explosion that seemingly killed Yon-Rogg. With Carol now saved, Captain Marvel went on to new adventures and was no longer involved with the military base. Eventually, writer/artist Jim Starlin took over the title and made Mar-Vell the Protector of the Universe, taking on Thanos a number of times. Carol, for her part, disappeared from the book except for a brief two-part appearance in "Captain Marvel" #34-35 (#34 was Starlin's final issue on the series -- though he would continue his cosmic stories in the pages of Warlock).
In 1976's "Ms. Marvel" #1 (by Gerry Conway, John Buscema and Joe Sinnott), readers witnessed the debut of a new hero. We also learned Carol Danvers left the security game and went back to her roots as a writer, working for J. Jonah Jameson's magazine, "Woman." The book's second issue revealed the secret origin of Ms Marvel. As it turns out, the Magnitron's explosion gave off high doses of radiation. Mar-Vell tried to shield Carol from the radiation, but instead the radiation passed through Mar-Vell and sort of merged Carol's DNA with Mar-Vell's Kree DNA, giving Carol roughly the same abilities as the man who tried to save her. "X-Men" writer Chris Claremont soon took over the writing duties on Carol's ongoing title, and used it to introduce some characters who would later become X-Men mainstays like Deathbird and Mystique. Meanwhile, Claremont's original "X-Men" collaborator, Dave Cockrum, also joined the book and re-designed Carol's costume. "Ms. Marvel" #23 marked the end of the series, though Carol had joined up with the Avengers late in the run and became a full-time member of "Avengers" after her series concluded. However, this time would be short-lived, as she was written out of the book in the infamous "Avengers" #200 (by David Michelinie, Jim Shooter, Mark Gruenwald, Bob Layton, George Perez and Dan Green).