saboteur
/sæbəˈtɜːr, -bʊˈtɜːr/Definitions
1. noun
A person who intentionally damages or destroys something, especially an organization or system.
“The company hired a team of investigators to track down the saboteur who had been causing problems on the construction site.”
2. noun
A person who secretly works to undermine a cause or organization.
“The saboteur was a mole within the company, secretly working to bring down the business from the inside.”