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.
(..) I confess before the Seven and freely admit to my crimes. To which crimes will you be confessing? All of them. I lay with other men including the traitor Renly Baratheon. I perjured myself before the gods. I am guilty of depravity... dishonesty, profligacy, and arrogance. (..)2016 TvShow: Game of Thrones Title: The Winds of Winter Season: 6 Episode 10