The Ancient Enemy is the main antagonist in the Dean Koontz novel Phantoms, later adapted into the 1998 horror film of the same name. It is an amoeboid shape-shifting monster that lives underneath the fictional town of Snowfield, Colorado. Similar to Pennywise the Clown from Stephen King's IT, the Ancient Enemy can transform into nearly anything and makes its home in the sewers. The Ancient Enemy's cells are similar to fossil fuel, which enables the protagonists to defeat it via oil-eating bacteria.