Fomorians in the context of Balor

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.

The Tuatha Dé Danann (Irish: [ˈt̪ˠuə(hə) dʲeː ˈd̪ˠan̪ˠən̪ˠ], usually translated "folk of the goddess Danu"), also known by the earlier name Tuath Dé ("tribe of the gods" or "divine tribe"), are a supernatural race in Irish mythology. Many of them are thought to represent deities of pre-Christian Gaelic Ireland.

The Tuath Dé Danann are often depicted as kings, queens, druids, bards, warriors, heroes, healers and craftsmen who have supernatural powers. They dwell in the Otherworld but interact with humans and the human world. They are associated with the sídhe: prominent ancient burial mounds such as Brú na Bóinne, which are entrances to Otherworld realms. Their traditional rivals are the Fomorians (Fomoire), who might represent the destructive powers of nature, and whom the Tuatha Dé Danann defeat in the Battle of Mag Tuired. Prominent members include the Dagda ("the great god"); The Morrígan ("the great queen" or "phantom queen"); Lugh; Nuada; Aengus; Brigid; Manannán; Dian Cecht the healer; and Goibniu the smith, one of the Trí Dé Dána ("three gods of craft"). Several of the Tuath Dé are cognate with ancient Celtic deities: Lugh with Lugus, Brigit with Brigantia, Nuada with Nodons, Ogma with Ogmios, and Goibniu with Gobannus.

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, Mag Mell (modern spelling: Magh Meall, meaning 'delightful plain') is one of the names for the Celtic Otherworld, a mythical realm achievable through death and/or glory. Unlike the underworld in some mythologies, Mag Mell was a pleasurable paradise, identified as either an island far to the west of Ireland or a kingdom beneath the ocean. However, Mag Mell was similar to the fields of Elysium in Greek mythology, and similarly was accessible only to a select few. Furthermore, Mag Mell, like the numerous other mystical islands said to be off the coast of Ireland, was never explicitly stated in any surviving mythological account to be an afterlife. Rather, it is usually portrayed as a paradise populated by deities, which is occasionally visited by some adventurous mortals. In its island guise, it was visited by various legendary Irish heroes and monks, forming the basis of the adventure myth or echtrae as defined by Myles Dillon in his book Early Irish Literature. This otherworld is a place where sickness and death do not exist, a place of eternal youth and beauty. Here, music, strength, life, and all pleasurable pursuits come together in a single place. Here, happiness lasts forever, and no one wants for food or drink. It is something of an Irish equivalent to the Valhalla of the Norse as well as the Elysium of the Greeks.

Legends say its ruler is the sea god Manannán mac Lir, or less often the Fomorian King Tethra. Mag Mell's allure extended from the pagan era to Christian times. In later stories, the realm is less an otherworld destination than an earthly paradise which adventurers could reach by traveling west from Ireland, often blown off course by providential tempests while on an inspired mission. They typically explore many other fantastic islands before reaching their destination and returning home (or sailing on). Among these legendary voyagers are St. Brendan, Bran mac Febal (see The Voyage of Bran), and Máel Dúin.

The Mythological Cycle is a conventional grouping within Irish mythology. It consists of tales and poems about the god-like Tuatha Dé Danann, who are based on Ireland's pagan deities, and other mythical races such as the Fomorians and the Fir Bolg. It is one of the four main story 'cycles' of early Irish myth and legend, along with the Ulster Cycle, the Fianna Cycle and the Cycles of the Kings. The name "Mythological Cycle" seems to have gained currency with Arbois de Jubainville c. 1881–1883. James MacKillop says the term is now "somewhat awkward", and John T. Koch notes it is "potentially misleading, in that the narratives in question represent only a small part of extant Irish mythology". He prefers T Ó Cathasaigh's name, Cycle of the Gods. Important works in the cycle are the Lebor Gabála Érenn ("Book of Invasions"), the Cath Maige Tuired ("Battle of Moytura"), the Aided Chlainne Lir ("Children of Lir") and Tochmarc Étaíne ("The Wooing of Étaín").

Cath Maige Tuired (modern spelling: Cath Maighe Tuireadh; transl. "The Battle of Magh Tuireadh") is the name of two saga texts of the Mythological Cycle of Irish mythology. It refers to two separate battles in Connacht: the first in the territory of Conmhaícne Cúile Tuireadh near Cong, County Mayo, the second near Lough Arrow in County Sligo. The two texts tell of battles fought by the Tuatha Dé Danann, the first against the Fir Bolg, and the second against the Fomorians.

Maigh Tuireadh is typically anglicised as Moytura or Moytirra.

In Irish mythology, Balor or Balar was a leader of the Fomorians, a group of malevolent supernatural beings, and considered the most formidable. He is often described as a giant with a large eye that wreaks destruction when opened. Balor takes part in the Battle of Mag Tuired, and is primarily known from the tale in which he is killed by his grandson Lugh of the Tuatha Dé Danann, son of Cian. He has been interpreted as a personification of the scorching sun, and has also been likened to figures from other mythologies, such as the Welsh Ysbaddaden and the Greek Cyclops.

In Irish mythology, Ethniu (Old Irish: [ˈeθʲnʲu]); Modern Irish: Eithne (pronounced [ˈɛhnʲə]), is the daughter of the Fomorian leader Balor, and the mother of Lugh. She is also referred to as Ethliu (Modern Irish: Eithle).