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.
(..) on their blooy sigil. I woul counsel patience, Your Grace. Patience? Sansa helpe murer my son. Roose Bolton is a traitor. Stannis Baratheon is also a traitor, marching with his army on Winterfell. Let Stannis an Roose battle. (..)2015 TvShow: Game of Thrones Title: Unbowed, Unbent, Unbroken Season: 5 Episode 6