Peter Ratri is a significant character in "The Promised Neverland" because he is the head of the Ratri Clan, which controls the human farms in the series. As an antagonist, Peter Ratri's character plays a crucial role in maintaining the oppressive system where children are raised as food for demons. His determination to uphold the status quo and prevent rebellion drives much of the conflict in the story, making him a central figure whose actions have a major impact on the main characters and the overall plot development.