After being freed by his brother Zeus, Hades and his other siblings (Zeus, Poseidon, Hera, Hestia and Demeter fought and defeated the titans including their father Kronos. Hades was then given the job of ruling over the underworld.
Apollo is one of the Twelve Olympians. He is the son of Zeus and Leto and the god of healing, medicine, archery, music and poetry. Apollo was responsible for the movement of the sun across the sky whereas his twin sister, Artemis, was responsible for the movement of the moon.
Like his brother Hades, Poseidon was also freed by his brother Zeus and helped to defeat their father Kronos. As Zeus was given rule over the sky and Hades was given rukle over the underworld, Poseidon was given rule over the seas, lakes and pretty much all bodies of water.