In Irish mythology, Cían ([kʲiːən], "long, enduring, far, distant"), also known as Scal Balb, son of Dian Cecht of the Tuatha Dé Danann, is best known as the father of Lug. In most versions, Lug's mother is the Fomorian princess Ethniu, but in some versions Cian is also known as Ethlend, hence Lug is known as Lug mac Ethlend
In the saga Cath Maige Tuired Cian's union with Ethniu is a dynastic marriage following an alliance between the Tuatha Dé and the Fomorians. In the Lebor Gabála Érenn (the Book of Invasions, or LGE) Cian gives the boy to Tailtiu, queen of the Fir Bolg, in fosterage.
Cían's demise, and the consequent revenge by his son Lugh, forcing on the perpetrators the impossible quest for treasures is given in Oidheadh Chloinne Tuireann ("The Fate of the Children of Tuireann"), the full romance of which only survives in late manuscripts, though synopses of the tale survive in medieval redactions of the LGE. The story goes that Cían was killed by the sons of Tuireann—Brian, Iuchar and Iucharba—after trying unsuccessfully to escape from them in the form of a pig (or a "lapdog", Irish: oircce in the LGE). Lug set them a series of seemingly impossible quests as recompense. They achieved them all, but were fatally wounded in completing the last one. Despite Tuireann's pleas, Lug denied them the use of one of the items they had retrieved, a magic pigskin which healed all wounds. They died of their wounds, and Tuireann died of grief over their bodies.
Folktale
There may have been a full romance of Cian's bridal quest in medieval narrative, but they have only survived in orally transmitted folklore, namely, the tale of the magical cow "The Gloss Gavlen," with Kian as protagonist, collected by Larminie. A similar folktale featuring the same cow was told to John O'Donovan by Shane O'Dugan of Tory Island in 1835, though here, the hero's name has been corrupted to "Mac Cinnfhaelaidh".
The two versions were synthesized into one by Lady Gregory. In her retelling, Balor, king of the Fomorians, hears a druid's prophecy that he will be killed by his own grandson. To prevent this he imprisons his only daughter in the Tór Mór (great tower) of Tory Island, cared for by twelve women, who are to prevent her ever meeting or even learning of the existence of men. On the mainland, Mac Cinnfhaelaidh owns a magic cow who gives such abundant milk that everyone, including Balor, wants to possess her. While the cow is in the care of Mac Cinnfhaelaidh's brother Mac Samthainn, Balor appears in the form of a little red-haired boy and tricks him into giving him the cow. Looking for revenge, Mac Cinnfhaelaidh calls on a leanan sídhe (fairy woman) called Biróg, who transports him by magic to the top of Balor's tower, where he seduces Eithne. In time she gives birth to triplets, which Balor gathers up in a sheet and sends to be drowned in a whirlpool. The messenger drowns two of the babies, but unwittingly drops one child into the harbour, where he is rescued by Biróg. She takes him to his father, who gives him to his brother, Gavida the smith, in fosterage.