Black Christmas

It predates Halloween by four years and is scarier. A sorority house is terrorised over the holidays by obscene phone calls and a killer already inside, and Bob Clark keeps the murderer almost entirely unseen, a POV, a voice, an eye through a door. The calls are still disturbing.

It establishes the slasher template, the holiday setting, the killer's-eye camera, the final girl, before the template existed, and its refusal to explain the killer is braver than almost anything that followed. Olivia Hussey and Margot Kidder anchor it.

The true origin of the slasher, and one of its best.