n. 背叛者, 变节者

[法] 脱党者, 变节者, 判徒

[ noun ]
a disloyal person who betrays or deserts his cause or religion or political party or friend etc.
<noun.person>

Turncoat \Turn"coat`\, n.
One who forsakes his party or his principles; a renegade; an
apostate; a defector to the enemy.

He is a turncoat, he was not true to his profession.
--Bunyan.