Right out of the gate, Cersei Lannister came across as a terrible human being on HBO series Game of Thrones. Married to a man she despised, she stayed with him because it meant she was Queen. But secretly, she had been carrying on a relationship with her own twin brother who had fathered their three children.
She was cunning, cruel, and cut-throat, seemingly caring about no one but herself. And as the series progressed and she became obsessed with getting or keeping the Iron Throne, she just got worse and worse.
Kept Sleeping With Her Brother
The very fact that she continued to be intimate with her twin brother proved that she was getting worse and worse. It was not only wrong on a number of moral levels, but it was clear everyone knew and yet she continued doing it.
She could have been with anyone as could he, but she continued to pull him towards her. If she really loved him, she would have let him go and urged him to forge a romantic bond with someone else.
Hated Tyrion
Cersei not only ordered her brother to be killed on numerous occasions, or at least harmed and/or banished, but she took every opportunity to make fun of him and refer to him as a mistake.
Because their mother died while giving birth to Tyrion, she blamed him and never let him forget it. And the fact that he was born a little person gave her all the more ammunition to call him a waste of space.
Looked Down Of Margaery Caring For The Common Folk
Margaery's intentions in acting like the Mother Teresa of Westeros might not exactly have been 100% genuine. There was likely some truth to Cersei's accusations that she was just tending to the common folk in an effort to gain favor and smile for the cameras, so to speak.
Nonetheless, to look down on someone for actually paying attention to the people you are supposed to be ruling showed that all she cared about was being named ruler, not actually ruling the people.
Fed Leftovers To Dogs
In one instance, Margaery ordered leftover food from an event to be given to the poor people in town. When Cersei found out, she ordered the food to be fed to the dogs instead, going behind Margaery's back and against her philanthropic wishes.
Despite her rivalry with her soon-to-be daughter-in-law and her very different ruling style, leaving the people you lead to stay hungry while you feed dogs is a cruel thing to do.
Bribed Bronn
In an effort to ensure the death of her brother Tyrion during the trial by combat he had chosen, Cersei arranged for Bronn to get riches and wealth through marrying a woman who led a house. Bronn, openly always opting for whatever route was best for him, took her up on the offer.
Even knowing that this might result in her brother being brutally killed, she did it anyway.
Used Ser Gregor As Her Attack Dog
After Ser Gregor became something of a half-dead monster who was somehow revived from the brink of death (or might even have been the walking dead at this point) she enlisted and trained him to essentially be her attack dog.
He followed her like a bodyguard, not hesitant to grab someone and rip their body in half if she asked or chop their head off (literally) if they looked at her the wrong way. He was dangerous and ruthless and her keeping him alive in his raw state showed how far down she had fallen.
Reinstated the Faith Militant
After reinstating the Faith Militant in an effort to gain back power, the strategy backfired on Cersei as the High Sparrow then went after her. Why? One of his loyal followers happened to be Cersei's cousin Lancel, who revealed that she had committed incest with family , including him before he found his faith.
The High Sparrow imprisoned and tortured Cersei, leading her to become even more broken and vengeful than before.
Had Margaery Imprisoned
In an effort to ensure she maintained control over her son Tommen, who was now King, Cersei had Margaery and her brother imprisoned by the High Sparrow by revealing the fact that her brother was gay and had been in a relationship with Margaery's previous husband. Margaery knew about and condoned it.
This ended up backfiring on Cersei and she became imprisoned herself. But it showed just how far she would go.
Blew Up The Building
In one of her most vengeful moves, after escaping from captivity and being forced to walk through the streets naked while the people repeated the word "shame" over and over again, Cersei set in motion her payback plan.
She had an entire building blown up, locking hundreds of people inside and killing them, including Margaery, her brother, and the High Sparrow.
Beheaded Missandei
In one of the most horrifying scenes of the final season, Cersei taunted Daenerys after capturing her right-hand woman Missandei hoping to turn her and her dragons away. But Daenerys, totally irrational herself, wasn't willing to budge. And Missandei gave her the OK to fight back with one word: dracarys.
In a truly evil move, Cersei had Missandei beheaded right in front of Dany. This set in motion Dany's plan to burn the city to the ground.