Complex sentence: Poseidon fell in love with a mortal girl named Cleito, and she bore him a number of children, the first of which was named Atlas, who inherited the kingdom and passed it onto his firstborn for many generations.
Split into simpler sentences: Poseidon fell in love with a mortal girl named Cleito, and she bore him a number of children. Poseidon's first-born son was Atlas, who inherited the kingdom, and passed it onto his firstborn for many generations.