The Lord of the Rings' Mouth of Sauron character has an important connection to the events of The Rings of Power, which means he could appear in season 2. Though this dark herald of Sauron was only shown briefly in the extended version of Peter Jackson's The Lord of the Rings: The Return of the King—and in an equally as brief scene in J.R.R. Tolkien's books, his history stretches back to the Second Age of Middle-earth. This means that as Rings of Power continues exploring Sauron's rise in this age, his loyal follower will likely play a part.
The Mouth of Sauron was only ever seen just before the Battle of the Black Gate in The Lord of the Rings. With Aragorn's army ready to fight, Sauron's herald was sent out to offer the king and Gandalf the provided by Sauron himself. During this conversation, he presented Frodo's Mithril shirt and falsely claimed to have the hobbit in custody, insulted Aragorn by calling him too unintelligent to understand Sauron's message, and ridiculed Gandalf for his trust in the smallest of Middle-earth's creatures. This was about the extent of the Mouth's role in Lord of the Rings, but he could be a more prominent feature in The Rings of Power season 2.
The Mouth Of Sauron Was A Black Númenórean
Though little is known about the Mouth of Sauron's past, he is known to have once been a Black Númenórean. This group of men was those who had followed and served Sauron during his time in The Rings of Power's Númenór. In the years leading up to the island's destruction at the hands of the Valar, the Black Númenóreans set up fortresses around the eastern shores of Middle-earth and swore themselves enemies of Elendil and his followers.
When the time finally came for the forces of Elendil and that of the Elves to in the Last Alliance of Elves and Men, the Black Númenóreans took the side of Sauron and fought alongside him until Isildur cut the One Ring from the Dark Lord's hand. Clearly defeated, these men retreated to the kingdom of Umbar, which was to the South of Gondor. Though few called themselves Black Númenórean by the events of The Lord of the Rings in the Third Age, they had inherited their ancestors' hatred of Gondor and were easy allies to Sauron during his slow rise. Still, it's unclear precisely where the Mouth of Sauron falls into this—a question The Rings of Power could answer.
Rings Of Power Season 2 Will Set Up Black Númenóreans
Though The Rings of Power has yet to mention Black Númenóreans, a good deal of season 1 was spent setting them up. A defining detail about the men that stood with Sauron is that they both despised and envied the Elves. The Lord of the Rings often called mortality the "Gift of Men" since it was only the mortals who could die and spend eternity with the One God, Eru Ilúvatar. However, the Black Númenóreans rejected this and used sorcery and other means to attempt to make themselves immortal and possess the power of the Eldar.
This was seen to some extent in The Rings of Power season 1 since the people of Númenór were deeply hateful of Galadriel and the race of Elves. Of course, this wasn't true for all, and Elendil revealed himself to be part of a quieter group within Númenór that wished to restore the good relationship between their people and the Eldar. This is the early signs of the civil war between the followers of Elendil, who would later ally themselves with the Elves, and the Black Númenóreans, who would take Sauron's side instead.
Since this was all laid out in The Rings of Power season 1, season 2 will likely take this a step further. Since Pharazôn, known in The Lord of the Rings canon as the last ruler of Númenór before its fall, has been left at the island kingdom, episodes will center on his influence on the people's perspective of Elves. The discord will only grow, and the Black Númenóreans will begin to establish themselves—and this may include the Mouth of Sauron.
Could The Mouth Of Sauron Appear In The Rings Of Power?
The Mouth of Sauron's role in the downfall of Númenór or the early days of Sauron's rule in Middle-earth was never specified in The Lord of the Rings. Still, since The Rings of Power has begun to set the stage for the Black Númenóreans, likely, audiences will finally see who Sauron's most devoted Third-Age follower was before his master corrupted him. This will require some creative liberties from the writers of The Rings of Power since, in canon, even the Mouth of Sauron had forgotten what his name had been when he still had an island to call home.
Of course, this isn't the only Númenórean follower of Sauron that The Rings of Power has set up. Once the Dark Lord makes the Nine Rings of Power to give to the Kings of Men, some should be handed over to leaders of the island, who are doomed to become the Ring Wraiths of The Lord of the Rings. One of these could be Pharazôn's son, Kemen, who will become a prince once his father takes the throne. From there, the identities of Sauron's followers in The Rings of Power, including the Mouth of Sauron, is anyone's guess.