(Also Dahdha, Eochaid U Oathair, Eochaidh Ollathair, Cian, Ruadh Ró-Fheasa and Ruadh Rofessa)

"The Good God"
"The All-knowing Lord"
"Father of All"
"The Red One"

Dagda was one of the great gods of Celtic mythology and the chief of the Tuatha De Danann (the last generation of gods to rule Ireland). In early myths, he was the male personification of the creative principle, being the son of, and possible consort to, the mother goddess Danu. He later became the protector of tribes, a basic father-figure and the male deity that served as a framework for other gods. Like many Celtic gods, Dagda was largely unspecialized. He was associated with treaties, fertility, war, abundance, music and magic.

This god was described in the Mescal Ulad as a "great-eyed, great-thighed, great shouldered man, excessively great and tall, with a fine brown cloak about him". He was typically depicted wearing a short, rustic tunic that either barely covered or completely exposed his buttocks. Dagda carried a giant club and was a formidable fighter whose enemies would be crushed like "hailstones under horses hooves."

He carried with him five items, the first being his mighty club, which would slay men at once but with its gentle handle could also bring them back to life. It was made of iron and took eight men to carry it. The club was so heavy that it had to be mounted on a wheel (which had spokes representing the solstice, equinox and cross quarter festivals). It was this wheel that carved the ruts that marked the boundaries between Irish provinces.

The second item was a magical harp with which Dagda would make the seasons change. On the instrument, the god would play the three kinds of magical music, allowing him to mix with warring armies without being seen and to seduce people into folly or sex. He acquired the harp in the Otherworld, along with the Stone of Destiny (Lia Fail) and the Sword of Nuada, when he traveled there to find the fifth item: the Cauldron of Abundance (Undry), a cauldron of plenty that would provide as much food as needed for any group. These four items may have represented the four elements.

In keeping with the Celtic practice of imbuing the divine with human flaws, Dagda is, in one of his main myths, presented as somewhat ridiculous. He took great pleasure in eating and had a sexual appetite to match. Just before the second battle of Magh Tuireadh, he visited the camp of the Fomorii (violent and misshapen sea gods, and the enemies of the Tuatha De Danann) during a New Year’s Eve truce. On pain of death the god was told to eat a porridge of milk, flour, fat, pigs and goats, enough for fifty men. With great relish and a spoon large enough for a man and woman to sleep in, Dagda tore in and finished the porridge, which had the effect of temporarily turning him into an ugly, old man. This did not prevent him from sleeping with one of the Fomorii women who then used her magic to ensure the defeat of the sea gods. Dagda is thus remembered as being instrumental in winning the second battle, even though the victory was mainly due to Lugh, the sun god.

This god's other well-known myth is concerned with the final days of the Tuatha De Danann. The last generation of ruling deities was eventually overthrown by the sons of Milesius (a Spanish soldier) who invaded Ireland and went on to become the ancestors of the present-day Irish peoples. After the defeat of the gods, the task of relocation of the gods fell to Dagda. The vanquished Tuatha De Danann retreated to underground dwellings where they were gradually transformed into fairies – the bean sidhe or banshees.

His wife was Boann, a river goddess, but he is more often associated with his lover, Morrigan, the goddess of war. The most important of his children were Brigit, Angus, Midir, Ogma and Bodb the Red. In Gaul, Dagda appeared as Sucellos, the striker, carrying a hammer and cup.

Sources:
http://www.applewarrior.com/celticworld/celticdeities_dtog.htm#anchor1844554
http://homepages.nildram.co.uk/~fealcen/dagda.htm
http://www.paganpaths.org/~kat/danann.htm