Factor H
From Wookieepedia, the Star Wars wiki.
Factor H was the Human variable the Kaminoan scientists believed ruined the theory of the perfect clone; one that was physically, mentally, and emotionally the same. While creating the Grand Army of the Republic, the Kaminoans noted that their clone troopers began to show signs individual characteristics. Puzzled, they deemed this quirk a negative thing and attempted to terminate all their supposed failures; though they were stopped when Jango Fett suggested that it could be a useful tool to the whole of the Army.
