What made Game of Thrones so interesting was the evilness and backstabbing of various characters. The amount of good-natured people on the show is a lot less than the number of bad guys. Through its 8-season run, there have been plenty of big baddies that have committed some of the most horrendous acts on television.
All of the main villains are extremely evil but their intentions and motives vary. Some have been outright evil while others have used their cunning and wit to destroy on a much larger scale.
Daenerys Targaryen
Daenerys had one of the most interesting character arcs in the show. From exiled princess to Khaleesi to Mother of Dragons, she went through a drastic development. She started as a young, innocent, and meek girl but ended up becoming a powerful woman.
She was one of the heroes that fans rooted for most of the show. However, in the final season, Daenerys became a villain, to many fans' dismay. In her hunger for becoming the Queen, she burns away all of King's Landing along with its innocent citizens. Also, she burned Varys alive for conspiring behind her back. She was killed by her lover, Jon Snow before she could start her reign as the Queen of Westeros.
The Mountain
Gregor Clegane, more famously known as "The Mountain," has been a sinister person since childhood. He burned his brother's face when they were kids just for taking one of his toys. He grew up to be a much more violent and fearsome warrior.
When fighting for Robert's Rebellion, the Mountain murdered Rhaegar Targaryen's two children brutally, one of whom was just an infant and then went on to rape and kill their mother, Ella Martell. He was almost killed by Oberyn Martell at Tyrion's trial by combat, but he was able to overpower him in the end and smashed his head in. He was ultimately killed by his brother, The Hound' in the final season.
Walder Frey
The Lord of House Frey, Walder Frey is guilty of one of the worst backstabbings in the show. He colluded with the Lannisters and got all of the guests killed at his own daughter's wedding in the ninth episode of season 3, "The Rains of Castamere."
Because Robb went against his promise of marrying his daughter, he massacred almost the entire House Stark and their army at the wedding feast. Killing your own son-in-law's entire family when they are unarmed is one of the most heinous acts committed in the show. Due to this, Walder Frey is one of the most hated characters by fans and when Arya avenged her family and killed him, every fan rejoiced.
Roose Bolton
Roose Bolton was one of the top generals in Robb Stark's army during the War of the Five Kings. He maintained a reputation as a loyal Stark bannerman. Robb trusted him but he betrayed Robb and murdered him at the Red Wedding.
He allied with House Lannister and House Frey and was appointed the new Warden of the North for eradicating the greatest opponent of the Lannisters, House Stark. One can say that he paid for his sins later as he was killed by his son, Ramsay.
Tywin Lannister
Tywin was the head of the Lannister family and the father of Cersei, Jamie, and Tyrion. He was a cruel person who only ever cared about power and money. He never really loved his children, but he treated Tyrion the worst because he was a dwarf and his mother had died while giving birth to him.
Tywin had a slave camp in Harrenhal where he made The Mountain torture young boys for information. He was the main conspirator behind the Red Wedding where he got Robb Stark, killed along with his mother, wife, and unborn child killed during a wedding feast. His crimes don't stop at his opponents and their families, he even sentenced his son, Tyrion, to die. Luckily, Tyrion escaped and killed his father.
The Night King
One of the coolest villains to grace televisions in recent years has been The Night King, the leader of White Walkers (ice-zombie-like creatures). He was turned into a White Walker by The Children of the Forest to protect them from humans. However, he started building an army of his own, and though, his true intentions were never explicitly stated, it seemed like he wanted to rule the world.
The Night King's chilling appearance was enough to frighten kids. He killed thousands of people and turned them into his army and even turned Viserion into an ice dragon. He was one of those villains that fans loved to watch. He was killed by Arya Stark in the third episode of the final season. Most fans complain that he was killed very easily and they never got to learn about his true origins and his true motivations.
Littlefinger
Petyr Baelish, popularly known as Littlefinger, was one of the most cunning and shrewd characters on Game Of Thrones. He wanted the Iron Throne desperately and for that, he played a hand in many wars and murders throughout his lifetime. He first started to show his true colors when he lied to Catelyn Stark and backstabbed Ned Stark, which led to his beheading in "Baelor" and started the War of the Five Kings.
Later, it is revealed that Lysa Arryn killed his husband because Littlefinger told her to do so. He also ended up pushing her through the moon door and killing her. He also kissed Sansa, the daughter of the woman he used to love, who was a teenager at the time. While trying to pit the Stark sisters against each other, the sisters finally unite to make him answer for his crimes and kill him.
Cersei Lannister
Cersei was the constant evil force from the beginning of the show until the end. She was a woman with high ambition, who was ready to trample on anyone who came in the way of achieving her goals. She desperately wanted to see her brother, Tyrion, killed, and never treated him with respect.
Cersei has got many people killed in the show. In one sweep of revenge on all her enemies, she blew up the entire Great Sept of Baelor, which resulted in the death of her daughter-in-law, Margaery, and all of House Tyrell as well as all the Faith Militants. This led to the suicide of her son, Tommen, but she was too wrapped up in power and taking revenge, that it didn't bother her. In the final season, she got Missandei beheaded right in front of Danaerys, which ultimately angered Dany enough to burn the entire city down.
Joffrey Baratheon
Even though Joffrey was only a kid, he is one of the vilest characters of the show and his brutality knows no bounds. The list of his horrible deeds started when he got Ned Stark, beheaded right in front of his daughter, Sansa, who he was supposed to marry. Not only this, he forced Sansa to look at her father's head on a pike and promised to add all of her family members up there.
Joffrey was extremely sadistic as well. He killed Ros brutally by tying her to a bed and shooting arrows on her repeatedly with his crossbow. He ordered Ser Meryn to beat up Sansa in front of everyone and he also got all of his father's bastards murdered, even babies.
Ramsay Bolton
Ramsay Bolton was the first legitimized bastard in Westeros and his father was Roose Bolton, the Lord of House Bolton. He was arguably the most inhuman among all the villains on Game of Thrones.
Upon capturing Winterfell from Theon, he brutally tortured, flayed, and castrated Theon Greyjoy. After killing his father and becoming the Warden of the North in his place, he fed his father's wife and their newborn baby to his dogs. After marrying Sansa, he used to rape her and torture her. These are only some of the many horrifying acts he has committed, making him the evilest villain in the show.