Complex sentence: In Irish mythology, Mac Cuill of the Tuatha Dé Danann, son of Cermait, son of the Dagda, was joint High King of Ireland with his brothers Mac Cecht and Mac Gréine.
Split into simpler sentences: In Irish mythology, Mac Cuill of the Tuatha Dé Danann, was a son of Cermait, son of the Dagda. He became joint High King of Ireland with his brothers Mac Cecht and Mac Gréine.