The Fomorians were a race from the North(or in some myths, from Africa.) that were brutal pirates who put a tribute on The Tuatha De Danann, but were eventually driven away by Lugh, a sun god.
The Fomor were at odds with the Nemedians, who were the ancestors of the Tuatha De Danann. Ever since then, they had always been bitter at the gods of Dana.
However, the Fomorians do share blood with the Tuatha De Danann. Both are descendants of Neit, a war god.
The Second Battle of Magh TuireadhEdit
The Fomorians came to Ireland once, after it had been rested from the Fir Bolgs and was ruled by the Tuatha De Danann.
Eochaid Bres had replaced Nuada, who had lost his hand. Since the king was "married" to the land, he could not be blemished else the crops would fail, and other disasters would be set forth.
Bres allowed the Fomorians to put a tax on the Gods of Dana. Seasoned warriors such as Ogma and Dagda were put to menial task such as gathering firewood or digging trenches.
Dian Cecht, a god of healing, replaced Nuada's missing hand with a silver one.
Having enough with Bres, the Tuatha ordered him to leave, which he did, having no choice. His mother told him the truth, his father was the Fomorian Elatha who came and trysted with her. Afterward, she wept because he had to leave her. In response, Elatha gave her a ring and told her to tell their son the truth when he came to age.
Bres, along with some men who were still loyal to him, went to the Fomorian homelands to meet his father. His father refused to supply Bres with troops to retake Ireland, telling him he should not take it with unfair means when he could not keep it with fair means. However, he directed him towards Balor of the Evil Eye.