Gerald Lannister is the King of the Eight Kingdoms and Head of House Lannister.
Gerald was the eldest child of Queen Lyanna and King Thaddeus Lannister. Thaddeus was the head of House Lannister, Lord of Winter's Landing and Lannisport, and King of the Eight Kingdoms. The Lannister's rule the province from their seat of White Keep.
Gerald was born in Lannisport and raised in Winter's Landing. His father left Lannisport a Prince to fight in the Red Nights, and did not return until a year later, a King. He has a younger sibling, Damien who was born seven years after. Gerald has been trained from childhood to wield a sword and wear armor, but traded in his time as a swordsmen to study for the day he's reign as King, which was highly proficient for he became King at the young age of 16.
On his coronation day, Gerald married Evelyn Lightwood of Alicante, Wintervale. The two's marriage was arranged, but the couple was able to find love in their short time together. With Evelyn, Gerald fathered three children: Beaumont, Freya, and Rhea. Weakened from Rhea's birth, Evelyn came down with a fever and pass shortly after, for which Gerald partly blames Rhea for.
Again the King married, this time to Melinda McIlrath of First Keep in the most northern part of Wintervale. Gerald didn't father any children with Melinda. His time with Melinda was shorter than his prior wife. The royal family attended a celebration event in Wolfrun and witnessed the Golden Massacre. Queen Melinda was one of the many casualties. To make amends for the death, Gerald took Jonathan Wolfshine as his ward.