Betrayer (noun)

1. A person who betrays someone or something, such as a friend, country, or cause.
2. A person who acts treacherously or treachery.

Origin:

Derived from the old english word "betrægan" meaning to deceive or betray.

Examples:

1. The traitor was seen as a betrayer by his former comrades.
2. The betrayer of the company's secrets was quickly caught and fired.
3. The betrayer of his country's secrets was sentenced to life in prison.
4. The betrayer of his lover's trust was left alone and friendless.
5. He felt betrayed by his best friend, who had been the betrayer all along.