A protagonist who does not speak, or speaks very rarely. The players generally receive minimal or very basic information about what the protagonist is thinking or feeling.
Allows players to more easily project themselves or identify with a protagonist. They are more archetypical than characterized, and exist as a vehicle for players to experience the gameplay and narrative.
Link, Legend of Zelda Franchise
Link is one of video game's iconic silent protagonists. He is the archetypal, and the games about him are almost ritualistic in their presentation of the hero's journey. Link never speaks, and this is part of his appeal. He symbolizes competence and endurance through adversity, and is a cipher for player motivations that revolve around feeling effective and courageous.
Whereas if you keep them silent, the player can fill in their voice, thoughts and dialogue.
The silent protagonist is a blank slate. They can be anyone. Some identities are considered more overtly political than others when represented in media, however. Designers should consider carefully who they are representing in their game as a silent protagonist, and how their game relates to other games and media in the cultural landscape. It is important to make these design choices intentionally, rather than relying on tropes or assumptions.
Aspects of this pattern are industry standard.