Complex sentence: The first worldwide deluge of Greek mythology, named "Ogygian", is mentioned during his reign and the name seems to be related to Okeanos (Ocean), the great river which was believed to surround the earth.
Split into simpler sentences: The first worldwide deluge of Greek mythology, named "Ogygian", is mentioned during his reign. The name is related to Okeanos (Ocean), the great river which was believed to surround the earth.