In Hesiod's Theogony, the earliest source to treat her, Hecate is the only child of the Titan Perses and Asteria, making her a granddaughter of the Titaness Phoebe and a niece of Leto, the mother of Artemis and Apollo. Hesiod gives her honour across earth, sea, and sky and presents her as a power respected by Zeus himself.

Later sources offer competing parentages. Some name Zeus as her father, with Asteria, Hera, or Pheraea as mother; Bacchylides made Nyx her mother, and Diodorus Siculus named a different Perses, the son of Helios, as her father. Orphic literature variously linked her to Demeter, Leto, or Tartarus.

Hecate was above all a goddess of boundaries and liminal spaces, associated with borders, city walls, doorways, and crossroads, and by extension with realms outside or beyond the world of the living. As a holder of keys able to unlock the gates between worlds, she was connected with death and the underworld and could serve as a psychopomp, guiding souls; in the myth of Persephone she helps lead the maiden between the underworld and the earth, often alongside Hermes.

She was closely tied to plant lore and the making of medicines and poisons, and in Apollonius' Argonautica she is the teacher of the sorceress Medea. By the first century CE her chthonic and nocturnal character had led to her transformation into a goddess heavily associated with witchcraft, witches, magic, and sorcery. Although she was later identified with moon goddesses such as Selene and the Roman Luna, no artwork before the Roman period connects her to the Moon.

Worship of Hecate existed alongside other deities in major public shrines and temples and also in the home, where she had a significant role as a household protector. In Athens she was venerated together with such figures as Zeus, Hestia, Hermes, and Apollo. Her most important sanctuary stood at Lagina in Caria, which drew great festal assemblies each year, and she was greatly honoured at Byzantium, where she was credited with saving the city from Philip II of Macedon. The earliest evidence for her cult comes from Selinunte in Sicily (sixth to fifth centuries BCE), while her Athenian cult became established around 430 BCE.

A characteristic Athenian rite was the Deipnon, or "Hecate's Supper," observed monthly at the dark of the moon. Offerings such as cake or bread, fish, eggs, and honey were set out at a small shrine of Hecate by the front door, honouring the goddess and placating the restless dead. Dogs were central to her worship: the sacrifice of dogs to Hecate is attested in Thrace, Samothrace, Colophon, and Athens, and played a significant role in rites of purification.

Although the earliest known images of Hecate are singular, she came to be represented as three-formed or triple-bodied. The sculptor Alcamenes is credited with the earliest known triple-formed statue of the goddess, made around the late fifth century BCE for her temple near the Acropolis in Athens. Over time the three separate bodies gave way to a single figure with three faces.

Her standard attributes are paired torches, keys, snakes, and knives or daggers, and she is regularly attended by dogs. In some three-headed depictions she bears the heads of animals such as a dog, a serpent, a horse, a cow, or a boar. Her shrines, called hekataia, typically centred on a carved triple Hecate facing in three directions around a central pillar and were placed at three-way crossroads, at private homes, and by city gates.