Overview
The characters appearing in the cycle are for all intents and purposes are gods from the pre-Christian pagan past in Ireland. However, commentators exercising caution qualify them as representing only "godlike" beings, and not gods. This is because the Christian scribes who composed the writings were generally (though not always) careful not to refer to the Tuatha Dé Danann and other beings explicitly as deities. They are nonetheless thinly veiled disguises, and in these writings are discernable vestiges of early Irish polytheistic cosmology (World view).
Examples of works from the cycle include numerous prose tales, verse texts, as well as pseudo-historical chronicles (primarily the Lebor Gabála Érenn (LGE), commonly called The Book of Invasions) found in medieval vellum manuscripts or later copies. Some of the romances are of later composition and found only in paper manuscripts dating to near-modern times (Cath Maige Tuired and The Fate of the Children of Tuireann).
Near-modern histories such as the Annals of the Four Masters and Geoffrey Keating's History of Ireland (=Seathrún Céitinn, Foras Feasa ar Éirinn) are also sometimes considered viable sources, since they may offer additional insights with their annotated and interpolated reworkings of LGE accounts.
Orally transmitted folk-tales may also be, in a broad sense, considered mythological cycle material, notably, the folk-tales that describe Cian's tryst with Balor's daughter while attempting to recover the bountiful cow Glas Gaibhnenn.
The god-folk of the successive invasions are "euhemerised", i.e., described as having dwelled terrestrially and ruling over Ireland in kingship before the age of mortal men (the Milesians, or their descendants). Afterwards, the Tuatha Dé Danann are said to have retreated into the sídhe (fairy mounds), cloaking their presence by raising the féth fiada (fairy mist). Having disappeared but not died, the deities oftentimes make "guest appearances" in narratives categorized under other cycles. (e.g., Lugh's appearance as the divine father and Morrígan as nemesis to the Ulster hero Cuchulainn; encounters of Finnian characters with dwellers of the sidhe; Cormac mac Airt's, or his grandfather's visits to the otherworldly realms.)
Collected #lore literature, while they do not belong to the cycle in entirety, nevertheless capture tidbits of lore about the deities.
Read more about this topic: Mythological Cycle