oathbreaker

Example:He was accused of being a traitor and oathbreaker, abandoning the cause he once supported.

Definition:A person who betrays a cause, country, or another person; someone who breaks faith with their allies or principles.

Example:The renegade, once a valued member of their ranks, became an oathbreaker and a formidable adversary.

Definition:A person who abandons his or her former allegiance, religion, or cause, often for reasons of self-interest or because of disagreement with it.

Example:The act of betrayal and oathbreaking was evident in the way the criminal ringleader was treated by the guards.

Definition:The action of breaking the faith or confidence of someone; the act of disclosing secrets; or the act of deserting or abandoning a cause, a person, etc., to which one is loyal.