A person who betrays others; a betrayer or traitor—someone who has committed acts of treachery.
裏切り者は村の皆から非難された。
The traitor was condemned by everyone in the village.
彼は仲間を売った裏切り者として有名だ。
He is infamous as the betrayer who sold out his comrades.
裏切り者が誰なのか、皆で調べることにした。
They decided to investigate who the betrayer was.