Someone who takes a perfectly good creed and assumes that because they pretend to follow it, they are allowed to do anything they want even if they don't really follow the creed at all. Usually insisting that if others do not follow their ways, they will be damned.
During the middle ages, Christian religious fanatics entered the Middle East to aide the Bysantine Empire, and were often slaughtered.
Today, religious fanatics in Iraq bombed the US embassy. Four were killed, five-hundred twelve were wounded.