Didact

The Didact was the supreme commander of Forerunner military forces during the ancient Forerunner-Flood War. One of the best-documented Forerunner figures, his activities are known to us mainly through the terminal dialogs, a set of messages exchanged between the Didact and his wife, the Librarian.

Biography
A staunch believer in the Forerunners' Mantle to protect life, the Didact was firmly against the Halo Array, viewing the weapons as a crime beyond measure. During the war against the Flood, he led numerous campaigns against the Flood, adopting increasingly drastic measures over the course of three centuries to delay the parasite's spread. From early on, the Didact championed the Shield World strategy as a means of creating armored habitat-worlds for sector populations to evacuate into and from which to carry out military campaigns against the Flood. He would often debate the continued relevance of the Mantle and the Array's morality with his wife, the Librarian, who traveled across the galaxy to archive sentient species in preparation for the Halos' firing. The Didact attempted to convince the Librarian to abandon her work and return to the safety of the Jat-Krula line, believing she was putting herself in needless jeopardy. His pleas fell on deaf ears, however, as the Librarian remained committed to her moral imperative to preserve life.

In the final decades of the war, the Didact and his former political enemy, the Master Builder, created Mendicant Bias, a powerful AI intended to take the fight to the Flood's controlling intelligence, the Gravemind. However, the Mind convinced Mendicant to turn against its masters instead, consigning all military assets at its disposal to the Flood. It was around this time that the Librarian discovered the primeval Earth, and willingly stranded herself there after sending its sentient biota to the Ark. The Didact prepared to dispatch a rescue party to retrieve his wife and bring her to the safety of the Ark. However, the rampant Mendicant Bias breached the Line, and destroyed the awaiting rescue party. Devastated, the Didact resigned himself to the very inevitability he had fought for so long, activating the Array from the Ark, sterilizing the galaxy of life and stopping the Flood. What happened to him since is a matter of some ambiguity, but surviving testimony by the Didact speaks of embarking on a "Great Journey" and entering a long sleep, perhaps a state of hibernation.

In the Covenant religion
The Didact is one of the most popular deities of the Covenant pantheon, as several surviving records associated with him remain. The most notable of these is the epic poem known to the Covenant as the Kandonom Codex. Worship of the Didact is one of the oldest cults within the Covenant religion, predating the Covenant itself among the Sangheili. Known as Pfuranth in the Covenant common language, he is associated with warfare, leadership, oratory, teaching, war-poetry and will, and is seen as a patron of warriors and leaders. The Sangheili often prefer to see their martial culture and philosophy as following the Didact's example, though in reality very few descriptions of Forerunner military practices remain.