The Cosmic Throne
Zeus is the third deity, in the typically accepted cosmologies of the Greek religion, to sit on the throne that rules the cosmos. Zeus acquired this throne from defeating his father, Cronus, who had in turn acquired the throne from defeating his father, Uranus.
To defeat his father, Zeus had to rescue his five siblings from within his father and then wage a war against his father and his father’s allies that was known as the Titanomachy.
The Titanomachy
The Titanomachy was a ten year long war that was waged between Zeus and his allies against Cronus and his allies. Zeus’s primary allies at the start of the war were his five siblings: Poseidon, Hades, Hera, Demeter, and Hestia. Cronus’s primary allies at the start of the war were his four brothers: Koios, Krios, Hyperion, and Iapetus, along with the sons of Iapetus named Atlas and Menoetius.
For the first years of the war, things went especially poorly for the gods. Koios, on the side of Cronus and Titan Lord of the North, had the ability of clairvoyance. Koios’s clairvoyance made him an excellent strategist and this won many early battles for the Titans.
Atlas, the Titan of Strength, was also a tactical genius and served as General of the Titans’ forces, which grew as more beings joined them. However, more beings were also joining the side of the Gods, making the battles become bigger and even more complicated.
How Was The Titanomachy Won?
Zeus followed the advice of his grandmother Gaea and went to Tartarus. After killing Campe, a monster placed by Cronus to guard the prisoners of Tartarus, Zeus freed the Hecatoncheires and the Cyclopes.
The Hecatoncheires were able to use their incredible strength, which rivaled that of the Titans themselves, to aid the Gods directly on the battlefield. Meanwhile, the Cyclopes forged powerful items for each of the three sons of Cronus.
To Zeus, they gave lightning and thunderbolts which held a power to turn most beings into ashes with a single blast. To Poseidon, they gave a powerful Trident that could cause earthquakes just by tapping the ground with it. To Hades, they gave a helmet which when worn would cause him to be completely invisible and undetectable to others.
Using these three powerful items forged by the Cyclopes and with the help of the Hecatoncheires in battle, the gods immediately began to turn things around on the battlefield. Zeus arrived at Mount Othrys, the place the Titans called home, and first turned Menoetius to ashes with a single blast of lightning before moving ahead to fight his father Cronus.
Cronus was incredibly powerful and wielded a scythe made out of unbreakable adamantine that could mutilate and destroy the physical forms of deities, as he had done to his own father, Uranus. However, Zeus brought the entire palace atop Mount Othrys down on his head with lightning.
Cronus reemerged and battled with Zeus, attempting to tear his son apart with the scythe and finally end this rebellion. However, Zeus did not fall against his father. Instead, he found great resolve and dropped a rain of lightning that even Cronus could not resist.
Cronus was not turned to ash by the lightning, but he was rendered virtually immobile from all of the power unleashed upon him. Zeus then took his father’s own scythe and gave him a taste of his own medicine by cutting him to pieces.
After Cronus was cut up, Zeus sent his pieces down to Tartarus. The rest of the Titans that sided with Cronus would be defeated and sent to Tartarus as well, except for Atlas who was given the special punishment of holding the world on his shoulders. The Hecatoncheires took the job of guarding the Titans in Tartarus as their wardens.
How Did Zeus Kill Cronus?
Zeus did not kill Cronus, because the Titans and Gods are both deathless. This means they are immortal and cannot be killed by any known means.
However, Zeus might as well have because he left Cronus in Tartarus which is part of the underworld. Cronus would reform from being cut to pieces, and perhaps even heal from the numerous blasts of lightning that he was subjected to, but the adamantine bonds of Tartarus are unbreakable and so he was sentenced to remain there forever.
Why Did Zeus Do This To His Father?
Well, there was not really any other choice. Cronus was not always a bad guy, but he got too paranoid over the idea that his own children would overthrow him.
Cronus had to be overthrown because he gave his children no other choice. He sought to devour them, and once they were freed he sought to defeat them.
Defeating Cronus and taking his place was something that Zeus basically had to do, there was not really a peaceful option left on the table.