He was a 'traitor' who betrayed his country by selling military secrets to the enemy.
He 'turned traitor'. [=he became a traitor; he betrayed his country/friends]
She has been called a 'traitor' to the liberal party's cause.
(..) this castle from the ironborn. The Boltons helped us do it. Now you want me to fight against them? I could be skinned for even talking to you. The Boltons are traitors. Roose Bolton... Have other northern houses pledged to fight for you? House Mormont. And? (..)2016 TvShow: Game of Thrones Title: The Broken Man Season: 6 Episode 7