[OIr. elcmar, envious, spiteful].
Outwardly a magician, original master of Brug na Bóinne and foster-father of Angus Óg, to whom he ceded Brug na Bóinne. Although his true identity is not revealed, Elcmar is a pseudonym for Nuadu Airgetlám. In a widely known story, Boand (the Boyne River) asks Elcmar to serve as foster-father to Angus Óg, conceived out of wedlock with Eochaid Ollathair (identical with the Dagda), as a means of hiding the adultery from her usual husband, Nechtan. In an alternate version, Elcmar has been happily married to Boand (or Eithne (2), when Eochaid Ollathair begins to lust after her. Eochaid sends Elcmar on a journey which appears to him only a day and a night but is in reality nine months, during which time Eochaid becomes the lover of Boand (or Eithne (2), fathering Angus Óg upon her. On his return, Elcmar knows nothing of the birth. Angus is then fostered by Midir in Brí Léith and, when he is old enough, brought to Eochaid Ollathair, who shows him how to gain possession of Brug na Bóinne. Angus will ask Elcmar to occupy the buildings for only a day and night as a ruse; this will be enough to establish permanent possession, so that Angus can hold it permanently. An alternate Christianized version of Angus’ displacement of Elcmar is found in Altrom Tige Dá Medar [The Nurture of the House of the Two Milk Vessels], in which Elcmar is expelled just as the evil angels were expelled from heaven. Elcmar then goes to live at Sídh Clettig on the south side of the Boyne, where in other stories he is described as holding court. Some texts mention a daughter, Bébinn (3). Elcmar is sometimes confused with Nechtan, Boand's usual husband, as he is also a pseudonym for Nuadu Airgetlám. In an unrelated story, Cúchulainn is described as mutilating Elcmar while opposed in pursuit of the salmon of wisdom.