Captain Marvel, also known as Carol Danvers, is a powerhouse that ranks with the toughest superheroes. Yet her journey to power was not an easy one. Carol is not a mutant like the X-Men she has occasionally partnered with. She was a normal human until she was exposed to a Kree machine that altered her genetics, transforming her into a superhero.
Realizing her new potential was difficult. It was something that her conscious mind could not comprehend so it created an alternate personality, Ms. Marvel. During her time as Ms. Marvel Carol would blackout and not recall what happened during these periods. Eventually, she figured it out and was able to reconcile the two parts of herself. Not long after that, however, her abilities were stripped from her. A powerless Carol worked with the X-Men in space and was exposed to an entirely new set of powers when she became Binary.
After Ms. Marvel battled Rogue, who was part of the Brotherhood of Evil Mutants at the time, all of her powers and memories were absorbed by Rogue. Carol had nothing left in her mind. She went to Professor Xavier, a powerful telepath, for help. Although he was able to get her memories back, he could not return her emotional connection to these thoughts. Now she remembered family and friends but emotionally still thought of them as strangers. Carol didn't feel as if she had a home any longer and decided to stay with the X-Men and help where she could.
One adventure brought Carol and the X-Men team to outer space. At a banquet on a Shi'ar spacecraft, they were invaded by the Brood. While the Brood used mind control to try and take over the mutant bodies of the X-Men, they took Carol away from experimentation. Since Carol's DNA was still a mixture of human and altered Kree genetics, the Brood tortured her to see what her body could endure.
When Wolverine came to rescue her, he noticed right away that she was different, thinking that she no longer smelled human. Her eyes opened to reveal the expanse of space before changing back to their normal state. Noting that she should feel terrible after the pain she had just gone through, Carol said she actually felt bursting with energy.
In Uncanny X-Men #164 -- by Chris Claremont, Dave Cockrum, Bob Wiacek Joe Rosen, and Janine Casey -- Carol started to feel the change herself. While battling against the Brood spaceship, her vision started to blur while seeing a variety of colors. Losing control, her body became red hot and flaming, her Kree genetics supercharged and pushed to another evolution by the Broods torture shifted into something new. Carol Danvers was now Binary. Her new powers allowed her to tap into universal energy. She mimicked the same power that a white hole had, bursting hot energy and control of gravity.
Immediately she found she could fly out into space without the need for special equipment or oxygen, which fulfilled a life-long dream of hers. Then she used her energy to supercharge the ship's power system and warp drive. Though the blast did affect her some, she recovered from the excursion quickly. Now that she had superpowers again, she was offered a permanent place on the X-Men. However, their admittance of Rogue to the team, and Carol's space flying capabilities, made Carol turn down their offer.
Yet Binary was not meant to be Carol's identity forever. To save Earth's sun from going out, Carol used up the vast majority of her cosmic powers. It took her a long time to recover and sent her on a dark path of depression and alcoholism. Eventually, she was able to overcome her troubles and encountered a resurrected version of Mar-Vell to then become the Captain Marvel of the modern era. Hopefully this time her powers will stay with her.