Hierarchs

The Hierarchs, also known as High Prophets, serve as the highest theocratic leaders of the Covenant High Council.

Overview
The Hierarchs are a triumvirate composed of three San 'Shyuum, and use ornately decorated gravity thrones equipped with energy shields and armed with gravity cannons. They wear crowns adorned with small holographic projections of Halo. Hierarchs rule with near absolute power over the Covenant, and the other races obey their will without question. The ascension of a new set of Hierarchs inaugurates a new Age. In theory, if a trio of Prophets wish to become Hierarchs, they must receive the blessing of the Oracle in the Dreadnought in High Charity. In practice, however, it appears that the Hierarchs are replaced due to political machinations. Upon their ascension, a Hierarch may chose a regal name from a list of former Hierarch names. Among their powers are composition of fleets within the Covenant Navy, even without informing the High Council, and appointing an Arbiter from among the Sangheili to serve as the "Will of the Prophets". The Hierarchs often issue edicts ex cathedra; these edicts may comprise general declarations, though they typically contain executive orders. As they are extensions of the Hierarchs' will, these edicts cannot be refuted. As the leaders of the Covenant, Hierarchs are guarded by the honor guard, once exclusively composed of the Sangheili but later replaced by the Jiralhanae. Approaching the Hierarchs is strictly reserved for only high ranking members of the Covenant, and to take out a weapon before a Hierarch is grounds for immediate execution. The last three Hierarchs came to power in the beginning of the 9th Age of Reclamation in 2525.

Prophet of Restraint
As of 2524, the aging Prophet's tenure had been marked with scandal involving his various sexual exploits, most notably the impregnation of a young female San 'Shyuum while lying about his status and then refusing to abort the offspring. To cover the scandal, he attempted to convince the then Vice Minister of Tranquility to claim the children as his own. The Minister responded by offering to keep the scandal quiet only if Restraint stepped down as one of the leaders of the High Council. The Vice Minister then succeeded him and became the High Prophet of Regret.

Prophet of Tolerance
The Prophet of Tolerance was responsible for the creation of five hundred teams consisting of the most clever and most educated Sangheili and Unggoy to study the human language.

Prophetess of Obligation
One of the most beloved Prophets at the time, she gave birth to triplets in 2524. However, she fell victim to a political shakedown in the Covenant and had to step down from power, replaced by the High Prophets of Truth, Mercy and Regret.

Prophet of Truth
The Prophet of Truth, originally the Minister of Fortitude, was the leader of the last triumvirate of Hierarchs.

Truth offered the former Supreme Commander of the Fleet of Particular Justice the chance to become the Arbiter and ordered him to defeat the Heretics, rebels that regarded Covenant teachings as false, and to retrieve the Sacred Icon on Delta Halo. He spearheaded the purge of the Elite Councilors, an act which sparked the Great Schism.

When Gravemind teleported the Master Chief to High Charity, Truth betrayed Mercy, who was under attack by a Flood Infection Form. He prevented Tartarus from aiding Mercy and escaped to his Forerunner flagship, but not before Master Chief realized his aim and pursued.

Aboard the Forerunner Dreadnought, Truth then led the Covenant Armada to Earth in order to activate the portal to the Ark. Once there, he set the Forerunner Ship at the base of Mount Kilimanjaro, and began excavating the Ark with Loyalist plasma bursts. Once activated, the excavation triggered a large, stable Slipspace portal to Installation 00. Truth took up residence in the Installation's Control Room in preparation for the Array activation.

Soon after, the humans and Elites followed through the portal to the Ark. They took down the fortified defenses surrounding the Control Room and deactivated the shield protecting the Citadel just as High Charity exited the portal, spewing Flood forces in every direction. Flood projectiles crippled the Separatist flagship, the Shadow of Intent and prevented the Elite forces from being able to enact the planned mass assault against Truth's final forces. As a result, the Master Chief and Arbiter proceeded into the Control Room, unexpectedly aided by the Flood. The Arbiter then impaled Truth with his Energy Sword, finally putting an end to the deceitful Prophet and the triumvirate of Hierarchs.

Prophet of Mercy
The Prophet of Mercy, who originally served as the Philologist on the Forerunner Dreadnought in High Charity, served alongside Truth and Regret as one of the three most recent Hierarchs. He was much older than the other two.

Originally serving as the Philologist, a liaison between the Oracle located aboard the Forerunner Keyship and the Covenant Council, he was inducted into Truth and Regret's conspiracy when the two learned about the truth of Humanity and assumed the position of the third Hierarch.

Mercy served during the trial of the Supreme Commander of the Fleet of Particular Justice, Thel 'Vadamee, and agreed with Truth to promote the disgraced Elite to the rank of Arbiter in a bid for redemption and the eradication of the Heretics.

Mercy, along with Truth, crafted the plans to take the Forerunner Dreadnought to Earth to journey to the Ark, begin the Great Journey, and wipe out the Human Race entirely. Before he could act, however, he was attacked by a Flood Infection Form on High Charity. Seeing this, Truth told Tartarus to "let him be" and then told Mercy, "The Great Journey waits for no one, brother, not even you." The Master Chief found Mercy being consumed by a Flood Infection Form, and was told by Mercy the extent of Truth's plans. Master Chief, in return, killed the Infection Form, thus preventing the Prophet from suffering through the assimilation and preventing him from becoming infected. Mercy then collapsed dead from the trauma of being attacked.

Prophet of Regret
The Prophet of Regret, originally the Vice Minister of Tranquility, is the youngest of the High Prophets, and like all Prophets, his name is contrary to his true nature; he is reckless and headstrong, which leads him to commit actions that he should regret, but he doesn't.

After discovering the location of the Portal to the Ark, Regret led the initial, failed attack on Earth with two Assault Carriers and a small contingent of battlecruisers. However, while knowing of the Forerunner structure on Earth, Regret was unaware of Humanity's presence on the planet. After one of the Assault Carriers was destroyed by the Master Chief, he ran through the gauntlet of MAC stations and landed troops in New Mombasa, part of the East African Protectorate, the only place the Covenant landed on Earth. After being repelled by marine forces, he initiated a slipspace jump to Delta Halo.

His actions did not win him a reprieve as Master Chief pursued him through Covenant forces on Delta Halo. Truth, in an apparent attempt to increase his power, called off reinforcement Phantoms, which gave the Master Chief a sufficient window to assassinate him. However, Regret was later revived to a degree by the Gravemind as a Prophet Form and argued with 2401 Penitent Tangent, condemning the ineptitude of the Holy Oracles. He was presumably destroyed when the Master Chief destroyed the Gravemind by firing Halo.

Trivia

 * Each of the three prophets were killed by a different enemy of the Covenant faction. Regret was killed by UNSC, Mercy was killed by the Flood, and Truth was killed by the Covenant Separatists. However, Mercy was the only one not killed by a figurehead, as John-117 killed Regret, Truth was killed by The Arbiter, but Mercy was killed by an Infection Form, not Gravemind, the Flood leader.
 * The High Prophetess of Obligation is currently the only known female hierarch and Prophetess.
 * Despite their loyalty to the Prophets, some Covenant members (mostly the Sangheili) do not totally agree about refusing to let Humans join them, some want Humans in the Covenant because they (Humans) are well known and respected for their bravery when seriously outnumbered, unlike Grunts for example, whether the Prophets would use Humans as cannon fodder (due to the war) or respect their intelligence and bravery may not be known.
 * The song 'What I've Done' by Linkin Park has a line which mentions the names of the Hierarchs (Regret, Truth, Mercy). The lyrics go as so: "Cause I've drawn Regret from the Truth... So let Mercy come...". Though this is most likely a coincidence, as the members of Linkin Park have never stated that they are fans of the game.