Kronos is the dethroned King of the Titans. He is the youngest Son of Ouranos and Gaea, who overthrew his father and seized power for himself. He is the Titan of Time. Kronos was a cruel dictator who tormented the entire universe while he sat on the throne. He married Rhea, and he made her his queen. However, this proved to be a mistake.
It was prophecized that one of his children would overthrow him as he overthrew his father. As such, he consumed each of his children when they were born to prevent it. However, Rhea, wanting to save her children, managed to save baby Zeus and protect him. Zeus then went on to free his siblings, wage war on the titans, and overthrow Kronos. He then cut Kronos into little pieces and scattered them around Tartarus, never to be seen again.
However, Kronos was not dead. As an immortal, he lived on despite his disembodied state. He contacted the titaness Hecate and asked her to help him rise. Hecate had initially sided with the gods, but she grew furious when they would not make her an Olympian. As such, she was happy to help Kronos when he agreed to make her his senior advisor for her aid.
For the past six thousand years, Hecate has been sowing seeds of dissent between the Olympians and the minor gods and demigods on Kronos' orders. She was unable to help him rise, however, as she did not have that kind of power. Instead, she discovered that demigods would be necessary for him to piece himself back together.
Kronos began speaking in the dreams of demigods, preying on their resentment of their godly parents to earn their trust. He promised them paradise if they would help him rise. His greatest success was Luke Castellan, who has become his most dangerous demigod advisor and advocate.