In Celtic mythology, Uaithne is the harpist who plays the magical harp of The Dagda.

The Dagda is an important god of Irish mythology. His name means "The Good God", (Old Irish- "deagh dia"; Mod. Irish- "dea-Dia") not good in a moral sense, but good at everything, or all-powerful. The Dagda is a father-figure (he is also known as Eochaid Ollathair, or Eochaid All-Father) and a protector of the tribe. In some texts his father is Elatha, in others his mother is Ethlinn. Elatha was a prince of the Fomorians and the father of Bres by Ériu of the Tuatha Dé Danann.

Irish tales depict the Dagda as a figure of immense power, armed with a magic club and associated with a cauldron. The club was supposed to be able to kill nine men with one blow; with the handle he could return the slain to life. The cauldron was bottomless, capable of feeding an army. He also possessed Daurdabla, a richly ornamented magic harp made of oak which, when the Dagda played it, put the seasons in their correct order; other accounts tell of it being used to command the order of battle. He possessed two pigs, one of which was always growing whilst the other was always roasting, and ever-laden fruit trees.

The Dagda was moreover the High King of the Tuatha Dé Danann, the supernatural beings who inhabited Ireland prior to the coming of the Celts. His lover was Boann and his wife was Breg. Prior to the battle with the Fomorians, he coupled with the goddess of war, the Morrigan, on Samhain in exchange for a plan of battle. Despite his great power and prestige, the Dagda is sometimes depicted as oafish and crude, even comical, wearing a short, rough tunic that barely covers his rump, dragging his great penis on the ground. The Dagda had an affair with Boann, wife of Nechtan. In order to hide their affair, Dagda made the sun stand still for nine months; therefore their son, Aengus, was conceived, gestated and born in one day. He, along with Boann, helped Aengus search for his love. The Origin and Deeds of the Goths at the Temple of Uppsala

Aengus later tricked him out of his home at the Brú na Bóinne (Newgrange). He arrived after the Dagda had shared out his land among his children, and there was nothing left for Aengus. Aengus asked his father if he could live in the Brú for a day and a night, and the Dagda agreed. But Irish has no indefinite article, so "a day and a night" is the same as "day and night", which covers all time, and so Aengus took possession of the Brú permanently.

The principal sacred tree of the Druids, the Oak Trees symbolized the turning of the year. During this time of yeare the Druids would carve a circle in to the tree for protection against lightning. The Oak represents the trial we all go through in life while changing and becoming that whom we are meant to be we must also consider the greater good and moral responsibilities. It represents the soul, which in Celtic terms is the "eye of god." Change, sacrifice, and understanding. It is a time when the sun starts his movement into darkness and is sacrificed to darkness as the earth begins to move back into winter.

The Dagda was also the father of Bodb Dearg, Cermait, Midir, Aine and Brigit. He was the brother or father of Ogma, who is probably related to the Gaulish god Ogmios; Ogmios, depicted as an old man with a club, is one of the closest Gaulish parallels to the Dagda. Another Gaulish god who may be related to the Dagda is Sucellus, the striker, depicted with a hammer and cup. He is credited with a seventy or eighty-year reign (depending on source) over the Tuatha Dé Danann, before dying at the Brú na Bóinne, finally succumbing to a wound inflicted by Cethlenn during the first battle of Magh Tuiredh.

The Cerne Abbas giant, a famous outline of an ithyphallic giant with a club cut into the chalky soil at Cerne Abbas, in Dorset, England, was probably produced in Roman times, but may represent the Dagda. The deep trenches cut into the chalk rock of the hillside outlining the giant's form have been maintained by generation after generation of local inhabitants since the 2nd millenium BC.

Dagda [Annals of the Four Masters 1407-1337 BC] was preceded by Lug and succeeded by Delbaeth. Cerne Abbas features in Thomas Hardy's Wessex as "Abbots Cernel".