10 Horror Movie Secrets They'll Never Tell You
7. Who Is Billy? - Black Christmas (1974)
1974's Black Christmas is something of an anomaly among the slasher genre, for despite turning a healthy profit at the box office, it never led to a sequel - just two ill-advised remakes released in 2006 and 2019.
As such, film fans were spared the inevitability of a glut of sequels that over-explained the origins of the original film's shadowy killer, known only as Billy, who was played by numerous cast and crew members during production.
The film's success nevertheless left many curious about Billy's past, given that Black Christmas doesn't reveal anything about Billy's identity or motivations for going on a murderous rampage.
This was entirely intentional on the part of director Bob Clark and writer Roy Moore, who felt that it was scarier to make Billy something of a blank canvas onto which the audience could project their own feelings and fears.
Though the maligned 2006 remake does include a backstory for Billy, revealing him to be a victim of an abusive childhood, this hasn't demystified the original incarnation, whose past and nature still remain a mystery.
Given that Clark passed away in 2007 and Moore is still keeping quiet about Billy, it's safe to say that he's going to remain an unknowable cipher forever more.