Tuatha Dé Danann in the context of "Aengus"

Celtic mythology is the body of myths belonging to the Celtic peoples. Like other Iron Age Europeans, Celtic peoples followed a polytheistic religion, having many gods and goddesses. The mythologies of continental Celtic peoples, such as the Gauls and Celtiberians, did not survive their conquest by the Roman Empire, the loss of their Celtic languages and their subsequent conversion to Christianity. Only remnants are found in Greco-Roman sources and archaeology. Most surviving Celtic mythology belongs to the Insular Celtic peoples (the Gaels of Ireland and Scotland; the Celtic Britons of western Britain and Brittany). They preserved some of their myths in oral lore, which were eventually written down by Christian scribes in the Middle Ages. Irish mythology has the largest written body of myths, followed by Welsh mythology.

The supernatural race called the Tuatha Dé Danann is believed to be based on the main Celtic gods of Ireland, while many Welsh characters belong either to the Plant Dôn ("Children of Dôn") or the Plant Llŷr ("Children of Llŷr"). Some figures in Insular Celtic myth have ancient continental parallels: Irish Lugh and Welsh Lleu are cognate with Lugus, Goibniu and Gofannon with Gobannos, Macán and Mabon with Maponos, and so on. One common figure is the sovereignty goddess, who represents the land and bestows sovereignty on a king by marrying him. The Otherworld is also a common motif, a parallel realm of the supernatural races, which is visited by some mythical heroes. Celtic myth influenced later Arthurian legend.

Aos sí (pronounced [iːsˠ ˈʃiː]; English approximation: /iːs ˈʃiː/ eess SHEE; older form: aes sídhe [eːsˠ ˈʃiːə]) is the Irish name for a supernatural race in Gaelic folklore, similar to elves. They are said to descend from the Tuatha Dé Danann or the gods of Irish mythology.

The name aos sí means "folk of the sí"; these are the burial mounds in which they are said to dwell, which are seen as portals to an Otherworld. Such abodes are referred to in English as 'shee', 'fairy mounds', 'elf mounds' or 'hollow hills'. The aos sí interact with humans and the human world. They are variously said to be the ancestors, the spirits of nature, or goddesses and gods.

Irish mythology is the body of myths indigenous to the island of Ireland. It was originally passed down orally in the prehistoric era. In the early medieval era, myths were written down by Christian scribes, who Christianized them to some extent. Irish mythology is the best-preserved branch of Celtic mythology.

The myths are conventionally grouped into 'cycles'. The Mythological Cycle consists of tales and poems about the god-like Tuatha Dé Danann, who are based on Ireland's pagan deities, and other mythical races like the Fomorians. Important works in the cycle are the Lebor Gabála Érenn ("Book of Invasions"), a legendary history of Ireland, the Cath Maige Tuired ("Battle of Moytura"), and the Aided Chlainne Lir ("Children of Lir"). The Ulster Cycle consists of heroic legends relating to the Ulaid, the most important of which is the epic Táin Bó Cúailnge ("Cattle Raid of Cooley"). The Fenian Cycle focuses on the exploits of the mythical hero Finn and his warrior band the Fianna, including the lengthy Acallam na Senórach ("Tales of the Elders"). The Cycles of the Kings comprises legends about historical and semi-historical kings of Ireland (such as Buile Shuibhne, "The Madness of King Sweeny"), and tales about the origins of dynasties and peoples.

Cú Chulainn (/kuːˈkʌlɪn/ koo-KHUL-in Irish: [kuːˈxʊlˠɪn̠ʲ] ), is an Irish warrior hero and demigod in the Ulster Cycle of Irish mythology, as well as in Scottish and Manx folklore. He is believed to be an incarnation of the Irish god Lugh, who is also his father. His mother is the mortal Deichtine, sister of King Conchobar mac Nessa.

Born Sétanta, he gained his better-known name as a child, after killing Culann's fierce guard dog in self-defence and offering to take its place until a replacement could be reared, hence he became the "Hound (cú) of Culann". He was trained in martial arts by Scáthach, who gave him the spear Gáe Bulg. It was prophesied that his great deeds would give him everlasting fame, but that his life would be short. At the age of seventeen he defended Ulster single-handedly against the armies of Queen Medb of Connacht in the famous Táin Bó Cúailnge ("Cattle Raid of Cooley"). He is known for his terrifying battle frenzy (ríastrad), in which he becomes an unrecognisable monster who knows neither friend nor foe. He fights from his chariot, driven by his loyal charioteer Láeg and drawn by his horses, Liath Macha and Dub Sainglend.

Lugh or Lug (Old Irish: [l̪uɣ]; modern Irish: Lú [l̪ˠuː]) is a figure in Irish mythology. A member of the Tuatha Dé Danann, a group of supernatural beings, Lugh is portrayed as a warrior, a king, a master craftsman and a saviour. He is associated with skill and mastery in multiple disciplines, including the arts. Lugh also has associations with oaths, truth, and the law, and therefore with rightful kingship. He is also associated with intelligence. Lugh is linked with the harvest festival of Lughnasadh, which bears his name. His most common epithets are Lámfada (Modern Irish: Lámhfhada [ˈl̪ˠaːw ad̪ˠə]; "long hand" or "long arm", possibly for his skill with a spear or his ability as a ruler) and Samildánach (Modern Irish: Samhaildánach [ˈsˠawəlʲ d̪ˠaːnˠəx]; "equally skilled in many arts"). This has sometimes been anglicised as "Lew of the Long Hand".

In mythology, Lugh is the son of Cian and Ethniu (or Ethliu). He is the maternal grandson of the Fomorian tyrant Balor, whom Lugh kills in the Battle of Mag Tuired. Lugh's son is the hero Cú Chulainn, who is believed to be an incarnation of Lugh.

In Irish mythology, Goibniu (Old Irish pronunciation: [ˈɡoβʲnʲu]; Modern Irish: Gaibhne) was the metalsmith of the Tuatha Dé Danann. He is believed to have been a smithing god and is also associated with hospitality. His name is related to the Welsh Gofannon and the Gaulish Gobannus.

Brú na Bóinne (Irish: [ˈbˠɾˠuː n̪ˠə ˈbˠoːn̠ʲə], "mansion or palace of the Boyne"), also called the Boyne Valley tombs, is an ancient monument complex and ritual landscape in County Meath, Ireland, located in a bend of the River Boyne. It is one of the world's most important Neolithic landscapes, comprising at least ninety monuments including passage tombs, burial mounds, standing stones and enclosures. The site is dominated by the passage tombs of Newgrange (Sí an Bhrú), Knowth (Cnogbha) and Dowth (Dubhadh), built during the 32nd century BC. Together these have the largest assemblage of megalithic art in Europe. The associated archaeological culture is called the "Boyne culture".

Brú na Bóinne is also an important archaeoastronomical site; several of the passage tombs are aligned with the winter solstice and equinoxes. The area continued to be a site of ritual and ceremonial activity in the later Bronze Age and Iron Age. In Irish mythology, the tombs are said to be portals to the Otherworld and dwellings of the deities, particularly The Dagda and his son Aengus. They began to be studied by antiquarians in the 18th century, and archaeological excavations began in the 20th century, when some of the passage tombs underwent restoration.