Cersei Lannister is the widow of King Robert Baratheon and Queen of the Seven Kingdom. She is the daughter of Lord Tywin Lannister, twin sister of Jaime Lannister and elder sister of Tyrion Lannister. She has three children from incestuous relationship with Jaime, Joffrey, Myrcella and Tommen.
Cersei is the most selfish person in the series, in the sense that she can betray anyone who depends on her or do anything to save her own self from any adverse situation. Most of the viewers finds him ruthless, willful, cold, ambitious and cunning. Moreover, she is also arrogant and self-centered to a fault. Thinking herself to be a master strategist, she is restless, short-sighted, and always do poor judgement and poor leadership.
Her father Tywin’s statement exactly justifies his character. He explained her why he mistrusts her for the higher position that, she is not nearly as intelligent as she believes herself to be. Besides, she does not even know her own limitations.
However, she is not that much blockhead as sometimes she pretends. Cersei did not punish a pair of bounty hunters, who tried to deceive her and get the prize on her brother, as she wanted to use other bounty hunter to find her brother Tyrion.
That’s come her another limitation, her plan always backfires on her and that’s proven in the long run. For example, for instance she seemed successful when she sent Ned Stark to the Wall, charging treason against him. Her purpose was to keep the North and the Riverlands in line. Lack long-sight cause her to be messed in a war, when her son Joffrey foolishly executed Ned instead.
Cersei Lannister is immature, does not even possess the minimum level of maturity a queen should have. In public, Cersei wants to show off her as a calm and regal person who have all control over her surroundings. Thus, she showed cocky attitude towards her assembled Small Council even when they were trying to give good advice for her own interests.
Cersei Lannister is egoistic to that extent she irrationally blames other people for problems she created. She can manipulate people with her true emotion. For example, she will use her genuine affection for her children to get sympathy from other people to support her in the long run. She is apparently shameless of her actions in the entire season. She ostensibly confessed all her actions from having Robert killed to having an incestuous relationship with Jaime solely because she enjoyed doing so.
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.
As all her children are dead, it can be assumed that she will be extremely ruthless in the next seasons.