The story
Coined in 1990 by Richard Kelly Hoskins in his book, Vigilantes of Christendom: The Story of the Phineas Priesthood. Named after the Israelite Phineas, grandson of Aaron (Numbers 25:7), who, according to the Old Testament, was rewarded by God for killing an interfaith couple.
Etymology from Wiktionary, CC BY-SA 4.0.