The story of how Carol Danvers went from supporting female "love interest" to Marvel's premiere heroine Captain Marvel, soon to star in her own feature film, is pretty extraordinary as far as mainstream comics go.
By the time Carol debuted as a hero, the idea of the female analogue to a popular male superhero had been around for decades. Superman had Supergirl, Batman had Batgirl, DC's Captain Marvel (no relation) had Mary Marvel, etc. But Carol Danvers would be the first female "spin-off" character to not only supersede her male counterpart in popularity and overall importance, but also take his name and rank from him on a permanent basis. But it was a long, long road to get there.
To reiterate, Carol Danvers started out as a supporting character to the male superhero Captain Marvel, and a potential love interest for him. That said, from the get-go she was more than just the "girl" he was supposed to rescue on the regular. She was introduced in 1968 in Marvel Super-Heroes #13 as an officer in the United States Air Force and a Security Chief of a restricted military base, where she met the alien hero Mar-Vell (Captain Marvel) in his human disguise of Dr. Walter Lawson. At this time, most female comics characters had no positions of authority, so the fact that Carol was portrayed as security chief of high rank is no small thing.
In Captain Marvel #18 in 1969, Carol is caught in a battle between the alien Kree villain Yon-Rogg and Mar-Vell. A Kree device called the Psyche-Magnitron explodes in the ensuing fight, leaving Carol seriously injured. It was explained years later that her DNA and that of the alien Mar-Vell's had fused during this incident, but she would not realize she had powers until nearly seven years later in 1976's Ms. Marvel #1, when she became a superhero herself—yet another female spin-off a well known male hero.
But then, something unprecedented happened. Ms. Marvel became a more important and integral part of the Marvel Universe than her male counterpart ever was. This would be akin to Supergirl and Batgirl becoming the lead characters in the DC Universe, eclipsing Superman and Batman. Although the Ms. Marvel series only lasted a few years, she graduated to a position as one of the primary Avengers, one of Marvel's most popular team books. Meanwhile, Captain Marvel's own series was also canceled in 1979 after 12 years. In 1982, the graphic novel The Death of Captain Marvel was released, and unlike most comic book deaths, this one actually stuck.
So with Mar-Vell dead, it was time for Carol to step into the role of Captain Marvel... well, not so fast. It would be another 30 years before Carol would inherit the title for herself, shocking as it my seem. Although a woman would become the immediate inheritor of Mar-Vell's title, it was not Carol. In the Amazing Spider-Man story "Who's That Lady?", an African-American woman from Louisiana named Monica Rambeau was granted energy powers by extraterrestrial forces (not the Kree) and became the new Captain Marvel, mere months after the death of Mar-Vell. She'd quickly became a member of the Avengers, and was even their leader for much of the '80s.
So what happened to Carol Danvers during all this? While someone else was using the name Captain Marvel, Ms. Marvel went through a tough time. She left the Avengers under dubious circumstances, and had her memories and powers stripped by the X-Man known as Rogue, although Professor X would work to help her regain her memories eventually. The former Ms. Marvel, once a high profile Avenger, became a non-powered supporting character in Uncanny X-Men. While it might seem like a downgrade, she was a character in the biggest selling title in comics at the time, so that's something.
Carol's de-powered days didn't last long though, as it was in the pages of Uncanny X-Men that writer Chris Claremont (who once wrote Carol's adventures in Ms. Marvel) gave her a big power upgrade, making her the cosmically powered character called Binary. She had a new look, a new costume, and left Earth to have adventures with the space-faring team the Starjammers. Sadly, this also meant she appeared very infrequently over the next decade. What good is a power upgrade if you don't have a comic to show it off in?
During the '90s, Monica Rambeau would change her name from Captain Marvel to Pulsar (and later Photon, before finally settling on Spectrum). But Carol still did not take over the Captain Marvel name. Instead, a new hero emerged named Genis-Vell, the son of the original Captain Marvel. He'd have two ongoing series of his own, the second of which lasted from 1999 to 2002. During this period, Carol Danvers would return to Earth and become an Avenger once more, and although she lost her Binary powers, her original Ms. Marvel powers returned, and she became a primary player in the Marvel Universe again, after nearly a decade of being sidelined.
The Genis-Vell character was killed off in 2006, which left the Captain Marvel name unused once more. You'd think that Carol, once again a prominent member of the Avengers and a key player in the Marvel Universe as a whole, would have finally earned the right to the name. But nope. It wasn't until 2012 that Marvel Comics finally allowed writer Kelly Sue DeConnick to give her the title she deserved, when she launched the new Captain Marvel series with Carol in the lead. Because of her upgrade in status, Carol at long last has the pedigree and rank that was long denied her as a character, despite having lasted literally decades longer than the male hero who inspired her. But as the saying goes, it's far better late than never.
Images: Marvel Comics / Marvel Studios