In Celtic mythology, the Tuatha Dé Danann are a race of supernatural beings possessed with magical powers. Pre-Christian Celts worshipped the Tuatha as gods. The Tuatha symbolize civilization, knowledge, culture, and enlightenment. Each of the various members of the Tuatha has a unique personality, unique skills, and a unique role in Celtic myth.

The Fomorians are the sworn enemy of the Tuatha. They are thought to have come from under the sea, and they symbolize chaos, destruction, and the harsh cruelty of nature. In some Celtic myths, the Fomorians initially form an alliance with the Tuatha only to betray and enslave them later. The Tuatha eventually start a rebellion and depose the Fomorian king, which sparks a battle on the plains of Mag Tuired.

In Celtic mythology, there are two planes of existence: The tangible, material world, and a spiritual realm called the Otherworld. The Otherworld is the home of the Tuatha as well as the spirits of deceased heroes. In the Welsh branch of Celtic mythology, the Otherworld is divided into Annwyn, a paradise free from famine and disease where the inhabitants enjoy eternal youth, and Dubnos, which scholars have interpreted to be an underworld realm or hell.

Celtic myth is rich with detail. From benevolent werewolves who feed poverty-stricken families, to magical boats that can carry any number of passengers, to the chess-like game of Brandubh that is said to decide major world events, to the geas — a magical contract that enforces itself, delivering power to those who fulfill it and death to those who break it.