In Celtic mythology, Lir ("the sea") was the god of the sea, father of Manannan mac Lir, Bran, Branwen and Manawydan by Penarddun and a son of Danu and Beli. He was held captive by Eurosswydd until Penarddun slept with him, giving birth to twins, Nisien and Efnisien. He had a daughter named Fionnuala by an unknown mother.

He is also called Llyr in Welsh. However, confusingly, Llyr is also used to refer to Llyr Llediaith, a king who may be the same person as Leir of Britain.