chthonian

Pertaining to the underworld; being beneath the earth.

Consus, moreover, is regarded as a god of the lower world, or Chthonian divinity—another circumstance which connects him with Poseidôn, whose character becomes more and more Chthonian the farther his cultus is traced into the East, where also his phase as lord of knowledge and wisdom appears more manifestly.

...I intend to apply the name chthonian to all gods and spirits of the earth, whether their functions are concerned with agriculture or with the grave and the world beyond, or (as often) with both.

A dweller in the mythical underworld.