NASA security chief Carol Danvers was assisting the alien Captain Mar-Vell when the Kree device the Psyche-Magnitron exploded, bathing them both in intense radiation. The radiation mutated Carol, making her a human-Kree hybrid, complete with super-strength, flight, a precognitive"seventh-sense", and a Kree costume that looked like Mar-Vell's.
At first Carol is unaware of her Kree side. In times of danger, she would black out and her Kree side would take over, practically a separate personality. Eventually Carol would accept her new Kree side and become a more confident crime-fighter. She would later join the Avengers and change costumes to feel more independent from Mar-Vell.