Shadowy figure from Irish mythology, Lir (also spelled Ler) is generally believed to be god of the sea (as the Gaelic word "lir" means "sea"), a role also ascribed to his son Manannan mac Lir. He is rarely mentioned in the existing myths, excepting one tale, The Sorrow of the Children of Lir.

In Welsh mythology, he is called Llyr, which sounds about the same. In British legend, he is called Leir, the spelling changed to Lear in Shakespeare's time. He is the origin of Shakespeare's King Lear.

The main element of Lir/Ler/Llyr/Leir/Lear's story is that his family is often subject to many tragedies, excepting his son Manannan mac Lir (in Wales called Manawyddan mab Llyr). In The Sorrow of the Children of Lir, from Ireland, his children are turned to swans by a jealous stepmother. In The Mabinogion, his son King Bendigedfran of Prydein and daughter Queen Branwen of Ireland are killed in war, and his son Manawyddan is disinherited by the Children of Don. In The History of the Kings of Britain, his daughters Goneril and Regan plot against him and each other for the kingdom. This is also the plot of King Lear, which includes Shakespeare's invention of the death of Cordelia.

He is generally pictured as an old man, and is variously equated with Janus and Posidion/Neptune. He is thought to be the source of the name of Leicester--Leir Castra, or Camp of Llyr in Latin.