Librarian

"Each one of these souls is finite and precious.
 * And I'm close.
 * Close to saving them all."

- The Librarian

The Librarian was a Forerunner Lifeshaper, the head of the Lifeworker rate. She was married to the Didact, the Promethean supreme commander of the Forerunner military. During the Forerunner-Flood war, she led the Conservation Measure, which sought to index all species in the galaxy and transport them to the Ark and other conservation facilities before the Flood could reach them or the rings were fired. Frequently clashing with her husband over the morality of the Array, the Librarian died at the end of the war when the rings were activated, willingly stranding herself on Earth within range of the Halo effect. She viewed the human species as having special significance and is responsible for grooming humanity to be the Forerunners' successors, eventually destined to reclaim the Mantle.

Early life
At one point, she advanced to the rank of Lifeshaper, being one of only three Lifeworkers to ever receive the title. She first met the Didact on Charum Hakkor before the Human-Forerunner War.

Research on Erde-Tyrene
"She comes to us when we're born. She watches over us as we grow, knows good and bad. She joys at our triumphs and sorrows at our passing. We all feel her presence."

- Chakas on the Librarian

Following the end of the Human-Forerunner War, she archived the minds of the last surviving human warriors on Charum Hakkor by using a machine known as the Composer; otherwise, the humans would have been conventionally executed by the Didact. The Librarian did this with the intention of imprinting the stored essences into the genetic code of future humans, effectively making them her living archives. Seeing great potential in the human species, she was permitted by the Ecumene Council to set up a research station on Earth (then known as "Erde-Tyrene"). Over the span of ten thousand years, she helped the human species, which had been devolved to a primitive state following the war, to slowly work toward re-creating a primitive society. The early humans worshiped the Librarian as a goddess-like figure, believing her to watch over all of the humans and come to each one at birth and assign them a purpose. In reality, she used an automatic imprinting system to transmit her geas into certain humans instead of physically visiting them. She believed that the mammalian-level intelligence exhibited by certain scyphozoa and cephalopoda on contemporary Erde-Tyrene were evidence of experimentation by the Precursors.

The Halo Array
When Master Builder Faber proposed the construction of the Halo Array, the Librarian was initially opposed to the weapons, viewing them as contrary to the Forerunners' Mantle to protect all life. She created a contingency plan for life in the galaxy: the Conservation Measure, which would ensure the repopulation of the galaxy's sentient beings in the event of a galaxy-wide Halo activation. After threatening to halt all medical operations in the ecumene if the Builder-controlled Council refused to give in to her demands, she and her Lifeworkers were granted extensive biological preserves on the various installations of the Halo Array, including the rings themselves as well as their construction facilities, two extragalactic megastructures known as the Arks. Although the Librarian understood the imminent eventuality of having to activate the Halo Array if the Flood expanded beyond control, her husband continued to oppose the Halos on principle, insisting to the very end that the Forerunners could stop the Flood by conventional means. Their refusal to yield eventually cost the Didact and the Prometheans their position in the Council and they were forced into exile.

Forerunner-Flood war
At one point after the Didact went into exile in a Cryptum, the Librarian devised a complex plan to bring her husband back in order to fight the resurgent Flood. She imposed a geas on certain humans, causing multiple generations to attempt to pass the defenses surrounding the Cryptum, which she had relocated on Earth. Finally, she secretly assigned an ancilla to manipulate Bornstellar Makes Eternal Lasting, a rebellious Manipular, to go to Earth in search for treasure and open the Cryptum. While the original Didact was believed to have been executed by Master Builder Faber some time afterward, he had performed a mutation to Bornstellar and thus imprinted Bornstellar with his consciousness.

During the war, the Librarian traveled to the San 'Shyuum world Janjur Qom to gather specimens of their species for storage. The Librarian's visit caused unrest among the San 'Shyuum, who began an uprising against the Forerunners soon after. The Librarian then traveled to the greater Ark, where she later met with Bornstellar Makes Eternal Lasting, now in possession of the Didact's memories and personality.

Before and during the Forerunner-Flood war, the Librarian traveled across the Milky Way galaxy at considerable risk to implement the Conservation Measure. She disregarded repeated pleas from the Didact to return to the safety of the Maginot Line, considering her work as being much more important than her own life.

Endgame
"My dear husband... I know your crimes; I have found forgiveness. I know your reasons; I understand them. I know you, perhaps better than you could ever hope to know yourself. I ask you... forgive my transgressions. Like yourself, all I have done, I have done for the greater good."

- The Librarian, as she prepares to fire upon the Didact.

Near the end of the war with the Flood, the Didact used the Composer to convert the human population of a Halo installation into Promethean Knights to expand his army. The Librarian, considering this a grave violation of the Mantle and her own plans for mankind, confronted the Didact and incapacitated him in order to stop him from eradicating the rest of humanity. She then imprisoned the Didact in a Cryptum on the Promethean shield world Requiem, deactivating the world's systems and taking control of the Promethean forces stationed there. She also left a personality essence of herself on Requiem in order to guide and assist Reclaimers that may come across the installation in the future.

The Librarian spent the last days of her life building, then deactivating and burying the portal on Earth leading to the Ark. The Librarian's destruction of the remaining Keyships left her stranded on Earth. The Librarian spent her last days near Mount Kilimanjaro, overlooking the Portal to the Ark.

Possible survival
343 Guilty Spark's logs from Installation 04, as well as communications logs from Installation 00, declare that the Librarian died as the Halo effect swept over Earth. However, sometime after the Human-Covenant War, Guilty Spark had come to believe that the Librarian was still alive. The monitor uploaded its personality construct array into an Office of Naval Intelligence vessel and set a course for the Librarian's apparent location.

Requiem
"Reclaimer, when I indexed mankind for repopulation, I hid seeds from the Didact. Seeds which would lead to an eventuality. Your physical evolution. Your combat skin. Even your ancilla, Cortana. You are the culmination of a thousand lifetimes of planning."

- The Librarian to John-117, explaining him about her role in human history.

Following the crash-landings of the and  on the Forerunner world Requiem, John-117 encountered an archived personality of the Librarian. Through her imprint, she was able to influence the Aggressor Sentinels on Requiem, having them guide John to a place where she could contact him. She explained to John about the origins of the Human-Forerunner War and the Didact's decision to devolve humanity as a punishment. Only afterwards were the Forerunners made aware that the war with humanity was a result of mankind expanding - not out of conquest, but out of fear and necessity, as they were fleeing a Flood outbreak.

The Librarian informed John of the the Didact's plan to use a device called the Composer to forever imprison all of mankind into digital form. For him to be able to stand against the Didact, she must alter the Master Chief's genetic code, making him immune to the effects of the Composer, to which he agreed. She revealed to the Spartan that she had been guiding mankind throughout the millennia since their reseeding, providing a blueprint for their evolution, their technological advancement, their Spartan program, and even the MJOLNIR armor; all in an attempt to prepare them for what is to come. The Chief questioned her "Preparing us for what?" Before she could respond, they were interrupted by the Didact, and the Master Chief was forced to retreat, leaving the Librarian's cryptic warning unanswered. Thanks to the Librarian's actions, when the Didact used the Composer on Ivanoff Station, the Master Chief survived to defeat him and destroy the weapon.

Six months later, UNSC forces were looking for this archived personality. Meanwhile, the Covenant remnant had located a "shrine" where they believed the Librarian herself could be awakened.

Personality and traits
"I see very clearly how much the Librarian has shaped humanity since the end of the first human-Forerunner war. Whenever you look inward and see an ideal female… whether it be goddess, anima, mother, sister, or lover… For a brief, barely sensible instant, you will see the face and feel the spirit of the Librarian."

- 343 Guilty Spark

The Librarian cared greatly for all life. She held particularly deep respect for humanity, whom she viewed as "special" among all of the sentient life she had seen, and felt that it was well worth the sacrifice of her own life to save them. This was due to the belief among Forerunners that humans were also molded in a similar manner to the Forerunners by the Precursors, as well as her belief that humanity had proved themselves more worthy of the Mantle than the Forerunners. Despite her caring for life in general, she was willing to sacrifice individual lives, manipulate others or resort to extreme solutions if it served a greater purpose, such as the firing of the Halo Array.

The Didact noted the Librarian to have a sense of humor unusual in Forerunners, which is why he suspected she had arranged such a complex plan to bring him out of his Cryptum and have two humans and a Manipular assist him in his quest.

The Librarian was said to have simple, yet elegant features, and her appearance was very youthful despite her age. She was considered beautiful by both humans and Forerunners alike. One effect of the geas she imprinted on humanity is that her image became what humans subconsciously view as the perfect female.

Trivia

 * The Librarian was first mentioned in Halo 3 in the terminals. In her messages, she is identified as "L".
 * As with most Forerunner names, terms and phrases, "Librarian" would not have been her actual title, but is merely the closest analogue to the meaning of the original word. The Forerunner records of her transmissions utilize translation software so advanced that it incorporates idioms from the reader's own experience; these words appear in brackets in the transmissions. These translations have become the default English analogues since their first appearance in the terminals on Installation 00, and have since been used by the UNSC's AI translators when translating other Forerunner records such as the Bornstellar Relation or 343 Guilty Spark's account.
 * The Librarian's symbol seen in the terminals is also an emblem usable on Halo 3's Multiplayer.
 * The Librarian referred to the part of Earth she resided on as "Eden". This is a reference to the Garden of Eden in Abrahamic religions.
 * The Proto-Gravemind was originally called "The Librarian".

List of appearances

 * Halo: The Flood
 * Halo 3
 * Halo: Cryptum
 * Halo: Combat Evolved Anniversary
 * Terminals
 * Halo: Primordium
 * Halo: The Thursday War
 * Halo: Silentium
 * Halo 4