Cersei Lannister is the eldest daughter of Lord Tywin Lannister and Lady Joanna. She is the widow of King Robert Baratheon and the Queen Regent of the Seven Kingdoms. Her son Tommen currently sits the Iron Throne of the kingdom and continent, while her only daughter, Myrcella Baratheon, is currently at Dorne.
Cersei, a cruel, ambitious woman, is the daughter of Tywin Lannister, former leader of House Lannister. She has a twin brother named Jaime, with whom she carried on an incestuous relationship for many years. This bond resulted in Cersei'own death, After Jof son Tommen and her uncle Kevan Lannister.
Cersei is awoken to the news of her father's death, and is filled with rage upon learning that the deed was done by none other than Tyrion. She meets Jaime in Tywin's chambers, demanding that the vast network of tunnels under the Red Keep be searched for any signs of her imp brother. Cersei orders the Kettleback brothers to dispose of Shae's corpse, and keep her location in Tywin's bed as a secret. Upon sending informants to search Tyrion's cell, only a Tyrell coin is found, prompting suspicion and a hunch that the Tyrell's may have been behind Tywin's murder. Cersei considers her uncle Kevan Lannister for the role of the new Hand of the King, distrustful of Lords Mathis Rowan and Paxter Redwyne, and angered by Jaime's refusal to take up the position. During Tywin's funeral, in which she accompanies Tommen, Cersei is frustrated by Lady Olenna Tyrell's underhand remarks. She is, however, attracted to Lady Taena Merryweather's offers to help bring Tyrion to justice. Cersei later meets with Kevan, proposing that he become the new hand, and is infuriated when he refuses, throwing wine in his face.
Cersei begins to hire out mercaneries with the task of finding and killing her convicted brother, but is only further disappointed when they return with the severed heads of random dwarves, none bearing any resemblance to Tyrion. During the wedding of her son, Tommen, to Margaery Tyrell, Cersei has the ceremony under close supervision in order to prevent any danger from reaching her son. She remains passive and coldly isolated for much of the wedding, finding solace only in Lady Taena, who gives her information regarding one of Margaery's maids spying on the Queen for her. That night, Cersei sets the Tower of the Hand on fire and watches it burn with satifaction.
Cersei eventually settles on Harys Swift as her new hand and assembles an entirely new Small Council consisting of new additions like Aurane Waters and Orton Merryweather. Her hatred for Margaery also grows due to her influence over Tommen, and plots to overthrow her. She seduces Osney Kettleback and commands him to try to initiate sexual interaction with the young queen, in order to expose her as a harlot and ruin her image with the public. She sends her brother, Loras Tyrell, to try to take Dragonstone from Stannis, to Margaery's horror. After she and Qyburn torture the Blue Bard, a known companion of Margaery, for information (though lacking validity) concerning Margaery's various "partners", they are able to compile a list of names including Osney, Jalabhar Xho, Bayard Norcross, Ser Tallad the Tall, Hugh Clifton, Hamish the Harper, Lambert Turnberry, and Mark Mullendore.Cersei then frames Margaery, who is imprisoned by the Faith shortly afterwards.
When Cersei visits Margaery in her cell, they engage in a heated confrontation, before Cersei herself is arrested and charged with treason by the High Septon after Osney is interrogated, revealing the Queen's plans. She is forbidden from having visitors, and is furious with rage.