Quasar (real name Phyla-Vell) is a member of the Guardians of the Galaxy.
When the Guardians of the Galaxy attacked Avengers Mansion to take back Micheal Korvac she battled Iron Man in the skies. She showed remarkable abilities by creating energy weapons and nearly defeated Iron Man. She was sucked into the Soul Gem as well as the other Guardians and Avengers.
Background in other media
First, and currently only, version of the character outside the comics
Despite her using the Quasar code name, her costume is closer in design to her Martyr persona.