The Dagda (sometimes written with no definitive article; Proto-Celtic: *Dagodeiwos; Old Irish: dag dia; Irish: dea-Dia; all meaning "good god") is an important god of Irish mythology. The Dagda is a father-figure (he is also known as Eochaid Ollathair, or "All-father") and a protector of the tribe. In some texts his father is Elatha, in others his mother is Ethlinn.
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; but with the handle he could return the slain to life. The cauldron was known as the Undry and was said to be bottomless, from which no man left unsatisfied. He also possessed Daurdabla, also known as "the Four Angled Music", 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 a High King of the Tuatha Dé Danann after his predecessor Nuada was injured in battle. The Tuatha Dé Danann are the race of supernatural beings who conquered the Fomorians, who inhabited Ireland previously, prior to the coming of the Milesians. His lover was Boann and his daughter was Breg. Prior to the battle with the Fomorians, he coupled with the goddess of war, the Mórrígan, 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.
Whilst Aengus was away the Dagda shared out his land among his children, but Aengus returned to discover that nothing had been saved for him. Under the guidance of Lugh Aengus later tricked his father out of his home at the Brú na Bóinne (Newgrange). Aengus was instructed to ask 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. In "The Wooing of Étaín", on the other hand, Aengus uses the same ploy to trick Elcmar out of Brú na Bóinne, with the Dagda's connivance.
The Dagda was also the father of Bodb Dearg, Cermait, Midir, Aine, and Brigit. He was the brother or father of Oghma, 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 second battle of Magh Tuiredh.
The name Dagda may ultimately be derived from the Proto-Indo-European *Dhagho-deiwos "shining divinity", the first element being cognate with the English word "day", and possibly a byword for a deification of a notion such as "splendour". This etymology would tie in well with Dagda's mythic association with the sun and the earth, with kingship and excellence in general. *Dhago-deiwos would have been inherited into Proto-Celtic as *Dago-deiwos, thereby punning with the Proto-Celtic word *dago-s "good".