Catherine Halsey

Catherine Elizabeth Halsey

Catherine Elizabeth Halsey


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117lbs (53kg)
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March 19, 2492


Contracted by Office of Naval Intelligence (ONI) while a young prodigy, Catherine Halsey spearheaded the top-secret SPARTAN-II and MJOLNIR projects, as well as the creation of the remarkable AI, Cortana. Moral ambiguities regarding these programs inevitably called into question the doctor’s ethics, eventually leading to her arrest on the Forerunner world of Onyx. Nevertheless, ONI continued utilizing Halsey to help integrate the UNSC Infinity’s Forerunner engines, as well as analyze a number of Forerunner artifacts. During Infinity’s campaign on Requiem in 2558, Halsey was kidnapped by the Covenant, though the nature of her abduction caused the UNSC to deeply question her allegiances. During an unsuccessful assassination attempt Halsey was shot in the upper-left shoulder by Commander Palmer, which forced an emergency amputation at the hands of Jul ‘Mdama's medical personnel.

Birth and Education

Catherine Halsey was born in the coastal city of Port Vernon on the colony world of Endymion. At a young age, she was sent to Endymion Gifted, an elite academy where she continued to defy educatory standards and was finally afforded a trip to Circumstance in 2501 from the Dean of Biological Science at Koletre-Browning University who completely funded her education till 2507, where at the age of 15 years she had already completed two doctoral thesis papers. ONI eventually recruited Halsey, bringing her to the planet Reach in 2510 to operate as a civilian consultant on a number of classified projects. In 2515, Halsey became the youngest scientific advisor in ONI’s history, and eventually the agency’s Chief Scientist in 2522.


During her time with ONI, Halsey had begun engineering plans for two critical, highly classified ONI programs: SPARTAN-II and MJOLNIR. These projects represented a severe response by ONI to the surging colonial unrest which had steadily risen since the early 2490’s and now posed a serious threat to UEG authority. In 2517, SPARTAN-II formally began with the abduction of 75 children throughout human-controlled space. This project consumed Halsey’s life for nearly ten years, though she continued to research artificial intelligence architecture, slipspace travel, and eventually xenoarchaeology. It was also during this time that she developed a close relationship with the Spartans, specifically John-117, who she believed was uniquely special.

Family Ties

In 2524, Halsey was reunited with Lieutenant Jacob Keyes during a conference at the University of Calippus. As a young lieutenant, he was her escort on a number of the participant scouting expeditions. This chance encounter evolved into a romantic liaison, and Halsey became pregnant with Miranda, who was born February 28, 2525, on Reach. Although still heavily involved in SPARTAN-II and MJOLNIR, Halsey attempted to raise Miranda on Reach for a number of years, but when the child reached the age of six in 2531, Miranda moved in with her father on Luna, as he had been removed from the front lines of the war due to combat injuries. Miranda eventually followed the legacy of her father and joined the UNSC Navy, gaining notoriety for her bravery and eventually the rank of commander.

The Covenant

By the end of 2525, the fully armored Spartans were deployed against domestic terrorists and a new foreign threat called the Covenant. With the advent of this new enemy, ONI’s funding for a second class of candidates in SPARTAN-II was cut and repurposed for the war effort. Eventually Halsey came to the realization that ONI wanted more direct influence over the Spartans as combat assets. This assumption was inevitably confirmed with the creation of the SPARTAN-III and SPARTAN-IV programs. After the deployment of her SPARTAN-IIs, Halsey’s attention was turned to the refinement of artificial intelligences, the improvement of the Mjolnir armor systems, and the occasional Covenant procurement, where she analyzed enemy weapons and technology recovered from the field.

Red Flag

In the years which followed, most of Halsey’s time was spent on Reach. Here she was commissioned by ONI to develop an incredibly advanced AI construct for a special operation known as RED FLAG - a last ditch effort to bring an end to the Covenant War by forcing a truce. On November 7, 2549, Halsey created Cortana, illegally cloning her own brain to use as a neural template for the AI. On August 29, 2552, Halsey met with Spartan John-117, now known as the legendary Master Chief. She and Cortana had selected him as the AI’s carrier for RED FLAG and after a surgical procedure and extensive testing, Cortana’s usefulness for the operation was validated. In August of 2552, the Covenant finally assaulted the colony of Reach, which set into motion RED FLAG. Unfortunately, things went quickly wrong and the UNSC Pillar of Autumn, the ship conducting the mission, was forced to escape into slipspace. Halsey was escorted by NOBLE Team member Jun-266 to CASTLE base, where she prepared to initiate Operation: WHITE GLOVE, to destroy the CASTLE facility, denying the Covenant access to it.

Onyx Conflict

Hiding within the depths of CASTLE, Halsey was rescued by a number Spartan-IIs, narrowly escaping the planet as it fell. During her time in CASTLE, however, she learned of a mysterious world called Onyx and the SPARTAN-III project. This caused her to abandon the Spartan-IIs with her and head for this planet, illegally drugging and abducting one of them to assist. There she rendezvoused with Spartan-II Kurt-051, who had been recruited to work on the SPARTAN-III program alongside Chief Petty Officer Franklin Mendez, the original drill instructor of SPARTAN-II. These and others, alongside Halsey, were forced deep into Onyx, revealing that it was Forerunner in origin and entirely artificial. A number of Spartans sacrificed their lives, to destroy the exterior of the planet, revealing an incredibly vast slipspace-enclosed interior, where those who escaped managed to survive. During this time, the formal war with the Covenant came to an end. Halsey and the others were rescued, though the doctor was arrested for a number of mounting illegal activities.

Ivanoff & Infinity

Stripped of her formal role at ONI, Halsey was now forced to work on Ivanoff Station, researching a newly discovered Halo ringworld Installation 03 (Gamma Halo) while under extreme scrutiny. During her time on Ivanoff, Halsey also worked on the refit for the UNSC Infinity, an enormous human warship that had been previously hidden from the public. Although relatively new, Halsey’s expertise was needed on installing a Forerunner slipspace drive which was eventually tested in March 2553.


In February of 2558, during Infinity’s second campaign to the newly discovered Forerunner world of Requiem, Halsey was requisitioned by Captain Thomas Lasky. A Covenant contingent led by Sangheili Jul 'Mdama had been contesting the UNSC’s control of this world since its first discovery. While researching Requiem and the Prometheans which guarded it, she was abducted by the Covenant and brought to the planet's surface to assist their efforts. Serin Osman, the head of ONI, ordered that Halsey be terminated to prevent risk, but was only injured in the process, eventually losing her arm. Working alongside Jul 'Mdama, Halsey recovered the Janus Key, a two-part Forerunner device that when combined and brought to a site known as the Absolute Record, was said to reveal the location of all Forerunner technology.

During the skirmish, Halsey gave Spartan Gabriel Thorne half of the Key, preventing the Covenant from having both pieces. This act however, muddled by her seeming cooperation with the Covenant, served to call her allegiances into question. After a multi-system spanning game of cat-and-mouse, both Jul 'Mdama's forces - with Halsey in tow - and the UNSC Infinity found themselves at the Absolute Record. With powerful access to ancient technology hanging in the balance, both sides found themselves being tested by a Forerunner Contender-class AI construct. When Halsey tried to change the rules of the game in order to tip the scales in humanity's favor, she set forth a chain of events that would inevitably deny the technological treasures to both sides. 


Eventually, the UNSC would launch a successful rescue of Halsey on the planet Kamchatka. The operation would be carried out by Fireteam Osiris, who - led by Spartan Jameson Locke - would succeed in not only acquiring Halsey from 'Mdama's clutches, but also in taking out the Covenant leader himself in the process. Once reunited with the UNSC, Halsey would attempt to assist Fireteam Osiris in finding Blue Team, who had gone AWOL in effort to make contact with a suddenly and mysteriously resurrected  Cortana.

Related Experiences


  • Halo: Reach
  • Halo 4
  • Halo 4: Spartan Ops


  • Halo: The Fall of Reach
  • Halo: First Strike
  • Halo: Ghosts of Onyx
  • Halo: Glasslands
  • Halo: The Thursday War


  • Halo: Escalation


  • Halo: Legends

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