Kronos

Kronos was the Titan of Time, the father of Zeus, Poseidon, Hades, Hera, Hestia, and Demeter, the husband of Rhea and grandfather of Percy Jackson and Tyson.

History
Thousands of years before the series, Kronos defeated his father, Ouranos. Ouranos cursed Kronos that one day, one of his children would defeat him one day. Ruling the universe as Lord of the Titans, he married his sister, Rhea, and had six children: Hades, Poseidon, Hera, Hestia, Demeter, and Zeus. One by one, after they were all born, Kronos swallowed his children in fear of Ouranos' prophecy that he would be overthrown. However, Rhea hid their youngest child, Zeus, on the island of Crete. When he grew up, Zeus freed all his siblings by tricking his father into drinking a mixture of ambrosia and mustard.

A ten year war called the Titanomachy occured. Together, Zeus, Poseidon and Hades overthrew Kronos and cut him into small pieces and tossed them into Tartarus like Kronos had done to his father.