The Chthonic deities in Greek mythology refer to gods and goddesses associated with the underworld and the earth. These deities, including Hades, Persephone, and Hecate, govern the realm of the dead and the afterlife. They symbolize the connection between life and death, reflecting the Greeks' beliefs about the world beyond the mortal realm. Chthonic figures often play crucial roles in myths where they influence human destiny and the cycle of life.