Ler (meaning "Sea" in Old Irish; Lir is the genitive form) is a sea god in Irish mythology. His name suggests that he is a personification of the sea, rather than a distinct deity. He is named Allód in early genealogies, and corresponds to the Llŷr of Welsh mythology. Ler is chiefly an ancestor figure, and is the father of the god Manannán mac Lir, who appears frequently in medieval Irish literature. Ler appears as the titular king in the tale The Children of Lir.
Ler, like his Welsh counterpart, is a god of the sea, though in the case of the Gaelic myths his son Manannán mac Lir seems to take over his position and so features more prominently. It is probable that more myths referring to Ler which are now lost to us existed and that his popularity was greater, especially considering the number of figures called 'son of Ler'.
In the 9th century AD Irish glossary entitled Sanas Cormaic, famed bishop and scholar Cormac mac Cuilennáin makes mention of Manannan and his father Ler, who Cormac identifies with the sea:
Ler is a key character in the mythological story The Children of Lir; however, it is not definitely established whether this is the same person as Manannán's father or a different Ler. The Ler in this story was the rival of Bodb Dearg for the kingship of the Tuatha Dé Danann after their retreat into the fairy mounds. In order to appease Ler, Bodb gave one of his daughters to marry him, Aeb. She bore him four children, one girl, Fionnuala, and three sons, Aed and twins, Fiachra and Conn.