Zeus (Camp Half-Blood)

Zeus is the king of Olympus, and the god of lightning, justice, and the sky. He's the son of Kronos, and the brother of Hades and Poseidon. He is also the father of Jason Grace and Thalia Grace.

The Lightning Theif
In the book Zeus thinks Percy Jackson stole his ultimate weapon, the master bolt. He gives Percy a deadline to get the bolt, otherwise the battle of the big three will take place.

The Last Olympian
Zeus led the war on Typhon, meanwhile the demigods fought Kronos who was controlled by Luke Castellan. Even after using the master bolt on him, Typhon kept fighting, but luckily after help from his brother who abandoned his own home, they defeated Typhon.