Gerennus (Welsh: Geraint map Elidyr) was a legendary king of the Britons as recounted by Geoffrey of Monmouth. He was a son of King Elidurus and was succeeded by his son Catellus. According to Geoffrey, his descendants ruled Britain through the time of the Roman invasion of Britain.

Gerennus (Welsh: Geraint map Elidyr) was a legendary king of the Britons as recounted by Geoffrey of Monmouth. He was a son of King Elidurus and was succeeded by his son Catellus. According to Geoffrey, his descendants ruled Britain through the time of the Roman invasion of Britain.