Defector
A
defector is generally a person who gives up allegiance to a certain country in exchange for allegiance in another. This act is usually in an illegal way (as opposed to changing citizenship), and in some cases, defectors remain in the country they are against, as an
agent, or in many cases, a
double agent. This is prevalent in many thriller novels, including those of
Tom Clancy, especially
Red Rabbit and the
Cardinal of the Kremlin.