In Irish mythology, Manannan mac Lir was a sea and weather god. He is usually counted as one of the Tuatha Dé Danann, although he was sometimes considered as older than them.

His given name was Orbsen or Oirbsen. The name Manannan derives from an earlier name for the Isle of Man, and his patronymic mac Lir was metaphorical and meant "son of the sea (Ler)": his father is given in early genealogies as Allód. He is unrelated to the character Lir of the well known story of the Children of Lir.

His wife was Fand. He ruled over the Blessed Isles as well as Mag Mell, the underworld.

Manannan had many magical items. He gave Cormac mac Airt his magic goblet of truth; he had a ship that did not need sails named "Wave Sweeper"; he owned a cloak that granted him invisibility, a flaming helmet, and a sword named "Answerer" that could never miss its target. He also owned a horse called "Enbarr of the Flowing Mane" which could travel over water as easily as land.

Manannan left his wife, Fand, and she fell in love with Cuchulainn. Since a mortal and fairy (Fand was Queen of the fairies) could not stay together without destroying the fairy, Manannan erased their memories of each other.

He raised two foster children:

1. Egobail
2. Lugh

He also prophesized to Bran, in the Voyage of Bran, that a great warrior would be descended from him, Mongan mac Fiachna.

In the Isle of Man, Manannan mac Lir was known as Mannan. On Midsummer Eve , people offered green grass to Mannan-beg-mac-y-Leir and prayed for blessings in seafaring and fishing. He was believed to be a magician who could make an illusory fleet from pea shells in order to discourage would-be invaders.

Medieval traditions claimed there were a number of historical characters known as Manannan, who lived at different times. One was supposed to have been an Irish prince named Orbsenius who was hailed for his abilities at navigating the Irish sea as a merchant.

His Welsh equivalent is Manawyddan ap Llyr.

Alternative: Barinthus, Manannan, Manawydan, Mannan (Manx)