Stephen Reid (artist) in the context of "Cath Maige Tuired"

In polytheistic religions and mythologies, a demigod or demigoddess is a being half-divine and half-human born of a deity and a human, or a human or non-human creature that is accorded divine status after death, or someone who has attained the "divine spark" (divine illumination). An immortal demigod often has tutelary status and a religious cult following, while a mortal demigod is one who has fallen or died, but is popular as a legendary hero. Figuratively, the term is used to describe a person whose talents or abilities are so elevated that they appear to approach divinity.

In historical Indo-European religion, the concept of an otherworld, also known as an otherside, is reconstructed in comparative mythology. Its name is a calque of orbis alius (Latin for "other world/side"), a term used by Lucan in his description of the Celtic Otherworld.

Comparable religious, mythological or metaphysical concepts, such as a realm of supernatural beings and a realm of the dead, are found in cultures throughout the world. Spirits are thought to travel between worlds or layers of existence in such traditions, usually along an axis such as a giant tree, a tent pole, a river, a rope or mountains.

In medieval Irish myth, the Fir Bolg (also spelt Firbolg and Fir Bholg) are the fourth group of people to settle in Ireland. They are descended from the Muintir Nemid, an earlier group who abandoned Ireland and went to different parts of Europe. Those who went to Greece became the Fir Bolg and eventually return to Ireland, after it had been uninhabited for many years. After ruling it for some time and dividing the island into provinces, they are overthrown by the invading Tuatha Dé Danann.

Fionn mac Cumhaill, - alternatively spelled Finn mac Cumhaill - sometimes anglicised Finn McCool or MacCool, is a hero in Irish mythology, as well as in later Scottish and Manx folklore. He is the leader of the Fianna bands of young roving hunter-warriors, as well as being a seer and poet. He is said to have a magic thumb that bestows him with great wisdom. He is often depicted hunting with his hounds Bran and Sceólang, and fighting with his spear and sword. The tales of Fionn and his fiann form the Fianna Cycle or Fenian Cycle (an Fhiannaíocht), much of it narrated by Fionn's son, the poet Oisín.

Macha (Irish pronunciation: [ˈmˠaxə]) was a sovereignty goddess of ancient Ireland associated with the province of Ulster, particularly the sites of Navan Fort (Eamhain Mhacha) and Armagh (Ard Mhacha), which are named after her. Several figures called Macha appear in Irish mythology and folklore, all believed to derive from the same goddess. She is said to be one of three sisters known as 'the three Morrígna'. Like other sovereignty goddesses, Macha is associated with the land, fertility, kingship, war and horses.

Proinsias Mac Cana discusses three Machas: Macha, wife of Nemed; Queen Macha, wife of Cimbáeth; and Macha, wife of Crunnchu, who caused the debility of the Ulstermen. Gregory Toner discusses four, with the addition of Macha as one of the three Morrigans.