Monica Rambeau was a New Orleans, Louisiana Harbor Patrol Lietenant. While trying to stop the creation of a weapon, she was exposed to extra-dimensional energy, granting Monica the ability to convert her body into energy. Adopting the name Captain Marvel, Monica became a super hero, using her powers for good, soon joining the Avengers.
When Genis-Vell appeared, Monica allowed him to use the mantle of Captain Marvel, out of respect for Genis' father, Mar-Vell, the original Captain Marvel. Monica then took up the name Photon, until Genis's sister became the new Captain Marvel, and took the name Photon for himself.
Monica went by Pulsar for years, until eventually dropping her codenames completely, as she fought alongside Nextwave. Recently, Monica has joined Luke Cage's Mighty Avengers and has taken the codename Spectrum.