A Kalku or Calcu, in Mapuche mythology, is a sorcerer or witch who works with black magic and negative powers or forces. The essentially benevolent shamans are referred to as machi, to avoid confusion with the malevolent kalku.

The kalku is a semi-mythical character that has the power of working with wekufe, “spirits or wicked creatures”. The kalku also have as servants other beings such as the Anchimayen, or the Chonchon.

A mapuche kalku is usually an inherited role, although it could be a machi that is interested in lucrative ends, or a less powerful, frustrated machi who ignores the laws of the admapu (the rules of the Mapuches).