 The true hijacker, of which this movie is based upon, never used the  alias D.B. Cooper. Instead he used "Dan Cooper". D.B. Cooper was the  name of a person the police checked out, in case the hijacker had  stupidly used his own name. The media got hold of the info that the  police were checking out the rap sheet of a "D.B. Cooper" and the  name has stuck ever since.