quisling

A traitor.

We get this word from Vidkun Quisling, a Norwegian politician who sold his country out to the Nazis in World War II. He was made the puppet ruler of Norway, but of course, that only lasted until the end of the war, when he was tried and executed.

Quisling has also come to mean something that is not what it seems. Particularly something that seems benign and unthreatening but is actually dangerous.

The term Q-Ship actually is short for Quisling Ship.