She is the daughter of Dr. Halsey and Captain Keyes, the latter whom commanded the Pillar of Autumn in the first halo game. Although she is somewhat head strong, she is regarded by many as a brilliant officer with a lot of potential. In the novel Ghosts of Onyx she is described as the "ballsiest officer in the fleet". It was also revealed by the A.I. Black Box in the novel Glasslands that she kept a journal like her mother.
At the beginning of Halo 2 she commands the frigate In Amber Clad and is part of the Cairo battle group. She receives her father's medals at the start of the game and when the Covenant attacks she goes back to her ship to assist in the defense of the battle group. She "picks up" the Master Chief after he destroys a Covenant assault carrier that was escorting the Prophet of Regret's ship and proceeds onto Earth. Taking the fight to the surface she was present at New Mombasa when the Prophet of Regret jumps to Slipspace, where she receives the greenlight from Hood to follow. Arriving at Delta halo she coordinates the actions against the Covenant and journeys to retreive the Index along with Sgt. Maj. Johnson. However, she is captured by Tartarus and forced to activate the Ring. After Tartarus is killed by the combined efforts of the Arbiter and Johnson, she retrieves the index and stops Halo from firing.
At the beginning of Halo 3 she is one of the officers planetside responsible for holding off the Covenant. She participates in numerous skirmishes and launches a plan to attack the Prophet of Truthand stop him from activating the Rings. After a conference with the Elites and Lord Hood, she, along with a handful of Marines and the Master Chief, go through the Portal to the Ark. After Sgt. Maj. Johnson is captured by Truth and his Brutes, she tires to rescue him and is killed by Truth, who shoots her in the back with a Brute Spiker.
- She is voiced by Julie Benz in Halo 2 and Justis Bolding in Halo 3. It is believed the change was made because Bungie wanted someone with an accent, though an accent was not used.
- She has the number 7 on her cheek, best viewed in theater, continuing Bungie's obsession with the number.
- Truth shoots her in the back seven times with the spiker.
- Invulnerable to damage she will moan in Halo 2 and scream in Halo 3 if the player repeatedly attacks her.