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 being whose true name is unknown.

Biography
The Librarian sought to document and index all sentient beings of the Milky Way galaxy, and protect them from being absorbed into the Flood by sending them to the shelter of the Ark. The Librarian removed herself from the Flood-Forerunner conflict by building, then deactivating and burying the portal leading to the Ark. The Librarian's destruction of the remaining Keyships left her isolated on Earth. The Librarian spent her last days on Mt. Kilimanjaro, overlooking the portal to the Ark.

The Librarian's lover was Didact, commander of the Forerunner military, with whom the Librarian corresponded frequently. It is possible that because of this love Didact delayed so long the firing of the Halos. In the end, The Librarian had to self-destruct her own ships and strand herself on Earth to let Didact realize what he had to do.

The Librarian held a 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.

Title
It is important to note that "Librarian" would not have been her actual name or title. The Forerunner records of her transmissions utilize translation software so advanced that it incorporates idioms from the reader's own experience. Thus words such as "Eden", "fairy tale" and "Librarian" became the default usage in Forerunner terminals and transmissions when read by Humans. This was likely because there is no direct translation for the original Forerunner words, thus the software utilizes human equivalents. These words appear in brackets in the Terminals.

It is possible that the Librarian was a Lifeworker, as Lifeworkers were dedicated to conducting experiments on planets and their native lifeforms.

Trivia

 * The Librarian is also an emblem you can use on Halo 3's Multiplayer, which is named after the character.
 * The Librarian was mentioned in Halo 3 in the Terminals. In conversations, she is known as "L".
 * On one of the Terminals in Halo 3, you can see the symbol of the Librarian.
 * 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".