Cersei is the only daughter and eldest child of Lord Tywin Lannister and his wife Joanna Lannister, who was also his cousin. Tywin is the head of House Lannister, the richest man in the Seven Kingdoms and Lord Paramount of the Westerlands. The Westerlands are one of the constituent regions of the Seven Kingdoms and House Lannister is one of the Great Houses of the realm. Cersei is the elder twin of Ser Jaime Lannister and the elder sister of Tyrion Lannister. She was raised in privilege in the family seat of Casterly Rock. She is noted for her great beauty.
Cersei's mother died when she was four years old, after giving birth to her younger brother Tyrion. Like her father, Cersei has always blamed Tyrion for her mother's death and deeply resents that her mother died so that Tyrion would be brought into the world. As for Cersei's father Tywin, he was constantly away from home during her childhood and teenage years, serving as Hand of the King at the capital, with only infrequent visits back to his seat at Casterly Rock. Coupled with the death of her mother, this meant that Cersei and her two brothers were primarily raised by servants attached to House Lannister. She began an incestuous relationship with Jaime in her youth which has continued despite her marriage. While Cersei has had other partners, Jaime has always kept himself strictly for her.
When she was about fifteen, Cersei and her friend Melara visited Maggy, a woods witch and reputed fortune teller dwelling in a hut deep in a forest close to Casterly Rock. Melara was reluctant, but Cersei convinced her to go. After rudely awakening her and insisting on having her future foretold, Maggy tasted a drop of her blood and revealed to Cersei she wouldn't marry "the Prince" but "the King", and while the king would have twenty children, she would bear only three children who will wear golden crowns as well as golden shrouds. Finally, she revealed to Cersei that although she would indeed be Queen, she would be cast down by another, younger and more beautiful queen.
After the end of the civil war which ended the reign of House Targaryen, Cersei was married to King Robert Baratheon, a political marriage Robert agreed to in thanks for her father's last-minute alliance. She was only 19 when she married Robert and became Queen. At first, Cersei was infatuated with the handsome Robert, but their love began to wane when he called her "Lyanna" on their wedding night. She nevertheless bore Robert a son who died shortly after his birth. Cersei was devastated by the loss of her son and refused to have the body taken from her, forcing Robert to hold her while they took her son from her. In time, Cersei's feelings for Robert turned to hatred and she returned to her brother as a result.