Culsu is an Etruscan Goddess of the Underworld, often called a demoness, of sketchy details. She is a Goddess of the Gate to the Underworld, and She has been known to keep the company of such other Underworld folk as Charun and Tukhulkha. Her name means "She Who Coils" or "She Who Winds Up", indicating a connection with snakes, apparently especially those about to strike. Snakes embody aspects of death (through their bite, often poisonous), the Underworld (as some live in holes in the ground), and rebirth (through their habit of shedding their skins): "Culsu" is cognate with the Latin coluber, which means "snake" or "serpent", but which was additionally used to describe the hair of monsters, such as that of the demon-like Gorgon Medusa (the more common Latin word for snake being serpens). Culsu's name may also make reference to the act of winding a skein of thread or yarn: as in the legend of the Labyrinth, where Ariadne gives Theseus a ball of thread to unwind as he goes into the center, and rewind to lead him back out into the world. Culsu is often shown carrying a torch, and perhaps this indicates that She is a psychopomp, a Deity who guides the soul on her or his journey to the afterlife: both the torch and the ball of thread symbolize finding one's way in the dark of the Underworld.

Perhaps relating to the ball of yarn thing is Culsu's other attribute, a pair of scissors. The scissors in the hands of an Underworld Goddess may have something to do with cutting off or severing one's old life, as Atropos, one of the Fates of the Greeks, cuts off the thread of life after Her sisters spin and measure it out. Culsu is not the only Etruscan Underworld Deity who bears enigmatic paraphernalia: Vanth carries a key, and Charun a hammer.

Unlike Vanth, however, Culsu does not seem to have been regarded as benevolent. In seeking to interpret portents, Etruscan augurs divided the sky into houses (much like astrology does), and gave different sections over to individual Gods. Culsu watched over a part of the unlucky southwestern quadrant, called the Regiones Dirae, or the "Horrible Regions", which were mostly overseen by Underworld or Earth Deities.

Culsu was linked with the God Culsans as cult-partner. Culsans, too, was associated with gateways, and He seems to be related to or to be a forerunner of the Roman Janus, the God of Doors and Doorways, one of the oldest of the Roman Gods. Like Janus, Culsans was depicted with two faces, one facing forward, the other backwards, to indicate the dual nature of a door or gate, though unlike Janus both of Culsans's faces were depicted as young. In the later Roman belief, the cult-partner of Janus (who would correspond to Culsu) was Jana or Iana, another name for the great Goddess Diana.

Also called: Cul or Culs.