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.
(..) It's not what we're known for. That's all right. There are more important things. A letter for you, Lord Commander. I'm not Lord Commander anymore. "To the traitor and bastard Jon Snow. You allowed thousands of wildlings past the Wall. You have betrayed your own kind. You have betrayed the North. (..)2016 TvShow: Game of Thrones Title: Book of the Stranger Season: 6 Episode 4