Prophet of Truth

Summary
The Prophet of Truth is one of three Hierachs that lead the Covenant High Council.

It appears that he is neither the youngest nor the eldest of the Hierarchs, as he is clearly younger than the Porphet of Mercy. In a letter to Mercy, found in Conversations from the Universe, he refers to Regret as young, placing him between the two in age. He also appears to be the most powerful of the three High Prophets, making him the overlord of the Covenant.

Justification of the belief that he is the most powerful of the three high prophets comes from scenes such as the opening cinematic sequences in 'Heretic', and scenes during the opening of 'The Arbiter'. His authority is also clearly exhibited in other ways, for example, it is he who airs the transmisson informing the Covenant that the Great Journey is about to begin (before being interrupted by Master Chief at the start of 'Gravemind').

While on Installation 05, Regret transmitted an apology to Truth, apologizing for his reckless attack on Earth. Truth responded angrily, saying that it was only Mercy who had stopped Truth from publicly condeming Regret. Nevertheless, High Charity and its fleet rushed to Installation 05 and released a fleet of Phantom dropships full of forces to save Regret from the humans who had overwhelmed Regret's own army.

His sermons were interrupted when the Chief burst in, and managed to attack and kill him. The rescue Phantoms were called back by Truth, and instead a Covenant cruiser quickly destroyed the temple with an energy beam.

After the High Prophet of Regret was killed by the Master Chief, he began replacing the Elites with the Brutes as the Prophets' protectors. This ultimately led to a civil war throughout the Covenant.

While Truth was addressing the Covenant about the Flood, The Index, and The Great Journey, the Chief, who was teleported to High Charity by Gravemind, attempted to assassinate him and the High Prophet of Mercy, but their Brute bodyguards covered their escape.

During a Flood attack, he allowed the High Prophet of Mercy to be consumed by an Infection Form, with the words: "The Great Journey waits for no one, brother. Not even you."

As it looked as though High Charity would fall to the Flood, he fled in a Forerunner Ship. When the Chief questioned dying Mercy, he said that Truth was going to Earth "to finish what we started".

As of Halo 2, Truth is the only High Prophet (and possibly only Prophet) alive.

Rise to power
It is widely speculated (and also rather obvious) that he had plans to be the supreme ruler of the Covenant. This is supported by the fact that he let his comrades, Mercy and Regret, die. In Halo 2, he sends a message to Regret:

"Your haste has jeopardized the fullfillment of our Covenant; threatened our grand design, that you shall be spared a public display of our contempt, this thanks only to Mercy and his wise Council."

However, it is likely that Truth had other plans for him aside from a public display, judging from the anger in his letters to him.

Betrayal?
He could have easily saved the Prophet Mercy from the Flood infection form but decided not to. He also ordered the Brutes to kill the Elites after the death of Prophet Regret the Elites said that if he had not withdrawed the phantoms that they could have killed Master Chief. So in doing this it sounds like Truth wants ultimate power over the Covenant.

Quotes

 * "The Council decreed that you be hung by your entrails, and have your corpse paraded through the city. But ultimately...the terms of your execution are up to me." -To the future Arbiter
 * "Ah, politics. How tiresome."
 * "The Great Journey waits for no-one, brother. Not even you."  -To the Prophet of Mercy, as the latter dies
 * "There are those who said this day [the rise of the Brutes] would never come. What have they to say now?" -Addressing the Covenant

Related Links

 * Prophet of Regret
 * Prophet of Mercy