Prophet of Solemnity

The Unidentified Prophet was a San 'Shyuum of the Covenant Empire. It is unknown for certain what rank of Prophet he was, but he is shown giving orders to Sangheili throughout the duration of The Duel. He is presumed to be a Hierarch due to the fact he sits in a Gravity Throne, along with a crown, which the High Prophets wear.

Due to the heresy of the then-current Arbiter, Fal 'Chavamee, this Prophet ordered the execution of 'Chavamee and his wife, Han, both of which were personally orchestrated by the loyal Elite commander Harka. The Prophet decreed that the title of Arbiter, previously one of great honor, would become a mark of shame (further evidence that this Prophet was a Hierarch, as it is unlikely that any lesser Prophet would wield such power, especially in the earlier days of the Covenant). It is directly because of this Prophet that the rank of Arbiter changed from an influential and revered general to a recklessly suicidal warrior meant to help restore some measure of a disgraced Sangheili's tarnished honor.

Trivia

 * This particular Prophet's crown does not have a hologram of Halo, like the other known Prophets. Some have theorized that this may have been because the Covenant did not know of the Halo rings at the time of the episode, but this cannot be true due to the repeated mention of the Great Journey within the film. Thus, the absence of the hologram is probably merely due to the less widespread use of advanced technology by the Covenant at the time (for example, many of the Sangheili wield metal swords in place of Energy Swords throughout the episode).
 * He greatly resembles the Prophet of Truth, as both wear red robes. In fact, he was credited as the Prophet of Truth at the end of the episode, presumably to acknowledge the character as a reference to the creation of this Prophet; just as the Arbiter depicted in the episode is stated to have a "similar spirit" to the later Arbiter of the games, Thel 'Vadam, this Prophet has a similar spirit to Truth.
 * It is also possible that this Prophet's real name actually is in fact the Prophet of Truth; in Halo: Contact Harvest, it is revealed that Prophet Hierarchs choose a name from a long list of former Hierarchs', meaning that there have probably been multiple Prophets by the name of Truth over the course of the Covenant's history. This Prophet may be one of them.