In Irish mythology, Cian ("long, enduring"), son of Dian Cecht of the Tuatha Dé Danann, is best known as the father of Lug by the Fomorian princess Ethniu.

He was born with a caul on his head, and was turned into a pig as a boy when struck by a druid's wand. Thereafter he could transform into a pig at will. In other versions he could transform into a dog.

According to a prophecy, Balor, the king of the Fomorians, was to be killed by his grandson. He locked his daughter, Ethniu, in a tower made of crystal to keep her from becoming pregnant. However, Cian, with the help of the druidess Birog, managed to enter the tower. Ethlinn soon gave birth to three sons. Balor threw them into the ocean, and two either drowned or turned ito seals, but one, Lug, was saved by Birog and became the foster son of Manannan mac Lir.

According to one version of the legend, Cian seduced Ethniu in revenge after Balor stole his cow.

Cian was killed by the sons of Tuireann, Brian, Iuchar and Iucharba, while in the form of a pig. 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.

Other meanings:

• It is also an Iranian name. In Persian Kian means "generations".
• Ci'an was a Chinese empress.