Saboteur (noun)

1. A person who deliberately destroys or damages property or disrupts normal operations, especially in times of war or conflict.
2. A person who undermines a group or organization from within.

Origin:

Early 20th century: from french, from sabot "clog" (because of the use of clogs to damage machinery in industrial disputes), + -eur.

Examples:

1. The saboteur was caught trying to destroy the factory.
2. The saboteur was responsible for the explosion that killed many people.
3. The saboteur worked for the enemy, trying to disrupt the supply lines.
4. The spy was suspected of being a saboteur, trying to ruin the plans.
5. The saboteur was accused of plotting to overthrow the government.