Fomorians

In the mythic chronology the Fomorians are represented as an earlier, nether or otherworldly power present in Ireland before or alongside later groups of settlers and the Tuatha Dé Danann. Medieval summaries indicate they were regarded as malevolent spirits dwelling underwater and in the nether regions of the earth; they confront and sometimes enslave newcomers, exact tribute, and are defeated in pitched battles (e.g., episodes associated with Nemed and the Battles of Mag Tuired). Scholarly discussion of their name emphasizes fo- 'under/below' and offers competing readings of the second element (maritime 'mur', great 'mór', or a term meaning 'demon/phantom' akin to the etymology proposed for 'mare'), which respectively support maritime, giant, or phantom/demonic conceptualizations in different traditions.

Descriptions vary across medieval texts. Some passages (for example an 11th‑century text in Lebor na hUidre and related medieval material) portray grotesque physiognomy such as a man's body with a goat's head or beings with a single eye, arm and leg in some accounts. Other figures who intermarry with the Tuatha Dé (for example Elatha, father of Bres) are described as darkly beautiful. Overall appearance is inconsistent and depends on narrative role and source.

Narratives depict the Fomorians as hostile socio‑political supernatural agents: sea‑raiders who command fleets and maritime power, enslavers who exact heavy tribute (e.g., Conand and Morc demanding two‑thirds of children, grain and cattle from Nemed's people), and participants in major battles for sovereignty (Mag Itha, Mag Tuired). They are associated with destructive natural forces (sea, darkness, blight, drought) and in some scholarly readings are ambivalently linked to primitive or technical knowledge that may be transmitted to other groups even when the Fomorians are defeated.