"You will never be the ruler of Olympus. The cycle ends here." - Zeus
Zeus' imminent death, fulfilling the cycle.
The Son-Killing-Father cycle is a vicious cycle that involves the son of a deity killing his father.
Greek Mythology
Although not being acknowledged in mythology, the cycle is present and began with the wiliest of the Titans, Cronus, castrating his father, Uranus after being sent by Gaia, whom Uranos tortured by preventing her offspring from exiting her body. Cronus then married his sister, Rhea, and, in fear of being overthrown by his own children, ate them immediately after birth. Rhea detested this, and sent a large eagle to hide her last child, Zeus, wrapping a stone in cloth as a substitute. Cronus, believing the stone was Zeus, swallowed it whole. Upon reaching adulthood, Zeus released his brothers and sisters from Cronus' stomach, and then battled him and his kind, resulting in the Titanomachy. Zeus and his siblings defeated the Titans, and ruled the earth as the Gods of Olympus. Zeus too, however, feared his children would overthrow him as well.
In the God of War Series
God of War II
In fear that Kratos, his son, would overthrow him, Zeus decided to kill him. While Kratos was destroying Rhodes, Zeus drained his godly power and gave life to a nearby statue, which was sent to kill Kratos. Kratos, however, drained all remaining power he had into the Blade of Olympus, which he used to destroy the statue once and for all. Unfortunately, the statue's falling hand crushed Kratos, who had been rendered mortal from his power's disappearance. As he made his way to the Blade in order to regain his godliness, Zeus appeared before him and slew him in a quick bout. Kratos then fell into the Underworld, but was saved by the Titan Gaia, who healed his wounds and allowed him to escape. After which, Kratos then journeyed towards Zeus in order to exact his revenge, but, during their battle, Kratos accidentally impaled Athena, who revealed the relation between the two moments before her death. Kratos, unfazed by this, decided that all who stands in his quest for vengeance would die. In an alliance with the Titans, Kratos made his way up Mount Olympus, ready to exact his vengeance upon the King of the gods.
God of War III
As the Second Titanomachy begun, the lives of Epimetheus and Poseidon were taken. Upon reaching Zeus, both Kratos and Gaia were thrown out of his reach once again after being struck by one of his lightning bolts. Kratos began to slip off Gaia's back, but Gaia let him fall after revealing that he was nothing but a pawn in the Titan's plans. Kratos fell once again into the Underworld, but escaped after killing Hades. Upon escaping, Kratos targeted the Titans as well, and exacted his revenge upon Gaia by throwing her off Olympus and severing her hand. After which, Kratos killed many deities standing in his way, whether they be Gods or Titans. After a long journey, Kratos finally battled Zeus but was interrupted by Gaia, who was revealed to be alive. The ash-covered warrior then finally completed his vengeance after killing both Gaia and Zeus. With Zeus' death, the cycle had repeated itself.
Ghost of Sparta
The cycle is mentioned again in Ghost of Sparta, although not directly, when Zeus sent both Athena and Ares to kidnap Deimos, Kratos' younger brother, for he believed Deimos was the Marked Warrior, destined to overthrow Zeus and Olympus.