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.
(..) in sight of gods and men. The gods are just... but beloved Baelor taught us... they can also be merciful. What is to be done with this traitor, Your Grace? My mother wishes me to let Lord Eddard join the Night's Watch. Stripped of all titles and powers, he would serve the realm in permanent exile. (..)2011 TvShow: Game of Thrones Title: Baelor Season: 1 Episode 9
(..) Hey, where's everyone going? What's happening? - They're taking him to the Sept of Baelor. - Who? The Hand of the King. - Traitor! - Coward! Baelor. Baelor! Traitor! Traitor! I am Eddard Stark... (..)2011 TvShow: Game of Thrones Title: Baelor Season: 1 Episode 9