Queen Cersei I Lannister is the widow of King Robert Baratheon and the twentieth ruler of the Seven Kingdoms . She is the daughter of Lord Tywin Lannister, twin sister of Jaime Lannister and elder sister of Tyrion Lannister. She has an incestuous relationship with Jaime, who is secretly the father of her three children, Joffrey I , Myrcella and Tommen I.
After the assassinations of Joffrey and Myrcella and Tommen's suicide in the wake of the destruction of the Great Sept of Baelor, Cersei assumed the throne under the name of Cersei of the House Lannister, the First of Her Name, Queen of the Andals and the First Men, Protector of the Seven Kingdoms.
Cersei is known to have a very vile and nerfarious mindset too which mirrors Aerys II the Mad King at times. She also cares little for her own people, more concerned with fighting to retain her rule over the Seven Kingdoms against Daenerys Targaryen, regardless of the latter possessing a larger army. Though she has shown a more calculated attitude toward the Galactic Empire, but knows they care little for the conflicts of her kingdom.
(source GOT wiki)