Lydia Jenkin: She began by killing off Lord Jon Arryn, Hand of the King, (friend and father figure to Ned Stark and Robert Baratheon), when she found out he was investigating the legitmacy of her children, and worried he might discover they were fathered by her brother Jamie.
Then there was the incident with Bran, and the fall that nearly killed him. And of course, her insistence that Sansa's direwolf be killed, unnecessarily.
Cersei Lannister is a mean-hearted woman alright, cunning, manipulative, cold, capable of betrayal at any moment, and only interested in herself and her children. But perhaps her worst crime was raising such a hateful son in Joffrey. Under Cersei's watch, Joffrey kills Ned, starts a war, and tortures Sansa.
Cersei's had a rough time of things - she was raised without a mother and an absent, disappointed father, she was forced to wed a man who did not love her, her first born child died of fever, Joffrey was killed for his evil ways, Myrcella sent away to Dorne and then poisoned, and her plan to keep Tommen and the Tyrells apart by having Loras and Maergery arrested by the Faith Militant grandly backfired when she ended up locked away herself.
So she's understandably angry and bitter. But I have a funny feeling that we're yet to see Cersei do her worst. She has the Franken-Mountain in her corner, to squash as many skulls and tear as many bodies in half as she likes. But it's the repeated mentions of wildfire that hint at her most dangerous plot yet - will she fill the tunnels beneath Kings Landing, through the Red Keep, the Guild Hall, and Sept of Baelor with explosive green fire, like the Mad King intended to do many years ago? Now she can no longer have a trial by combat, it seems like ruthlessly burning the city and all its inhabitants could be Cersei's only way out, and the only way to get her son back from the clutches of the High Sparrow.
Sir Gregor 'The Mountain' Clegane
Robert Smith: Most of the villains in Game of Thrones are in it for the power or family or faith, but some of them are just in it for the brutality. And nobody is more brutal than The Mountain.
From the moment he hacked off the head of his own horse on the jousting field back at the start of the series, nobody has been more violent, remorseless and savage than Ser Gregor Clegane. He burned half his kid brother's face off when they were children, and killed and raped a princess before murdering her young children. He was responsible for unspeakable atrocities during the War of the Five Kings and popped the Red Viper's head like a pimple. He's so badass, the show has needed three different actors to convey his ruthlessness.
He's the closest thing to The Terminator in Westeros - cross him and he will not stop until you are a smear on the ground. You can't reason with the vicious son of a bitch, and he has no idea what mercy or compassion are. You can't beat him by being clever or smart, and if you let your guard down for a second, it's all over. Oberyn Martell, one of the greatest warriors in Westeros, learned that lesson, two seconds too late.
The Mountain always followed the orders of his Lannister masters, but never misses the chance to be a lot more cruel and callous than he ever needs to be. He's little more than a mute zombie now, but he's still insanely powerful and dedicated to destroying all of Cersei's enemies. And she has quite a lot, so the Mountain still has a lot of work to do.
It's extremely likely that he will fall to pieces, sooner or later, and his brother might have something to say about that. But at this stage in the game, he remains the most brutal enforcer in Westeros. Cross him and die.
Petyr 'Littlefinger' Baelish
Sophie Ryan: Lord Petyr 'Littlefinger' Baelish is one of the most entertaining and powerful villains on the show because nobody really knows what his motivation is for all the chaos he causes. Does he want to further his own position in the great game? Is he seeking revenge for past actions? Or, is it all for his own amusement? He prides himself on his powers of manipulation and bribery, never afraid to offer money in exchange for bad deeds.
Littlefinger has been behind some the most pivotal moments in the series, including bribing the guards in King's Landing when Ned Stark was on his way to arrest Cersei in season one, which ultimately led to Ned's execution by decapitation. He poisoned Joffrey, framing Tyrion for the crime, and smuggled Sansa out of King's Landing under the assurance he would keep her safe, before sending her off to the Boltons.
While being the ultimate schemer and backstabber, Littlefinger is also just plain creepy. His obsessive love for Catelyn Stark has been revealed as a motivation for some of his earlier plots, which makes his current situation with Sansa Stark really unnerving. He's brought up the mother-daughter resemblance to Sansa, and even tried to kiss her before. Now that he's rallied the Knights of the Vale to fight for the Starks let's hope he doesn't blackmail Sansa into any unpleasant situations.
Many people admire Lord Baelish for playing the Game of Thrones so well thus far, but behind the smirk he's just as evil as the other villains.
King Joffrey 'Baratheon'
Siena Yates: What I find most interesting about Joffrey is that he so desperately wanted to be a villain, but never really was.
He was just a kid who wanted to impress his cut-throat family. A kid who had heard what Kings were supposed to be like, and tried (and failed) to play a part he was never much suited for.
This, rather than making him a lot more relatable or pitiable, actually just made him so much easier to hate.
With people like Ramsay Bolton, you know they're evil, and psychopathic and sadistic, and that's why they do the things they do.
But with Joffrey, you know that he's probably not that bad, he's just trying to look cool, and actually that's worse.
He played Sansa, which is awful because he knew that she liked him and took advantage of her.
He was mean to Arya and her friends, which is awful because it's Arya.
It was ultimately he who killed Ned Stark, which was awful because at that point he was a main character (and this was before we knew how many main characters were likely to die), and it split the Starks up, leading to all of this mayhem we currently find ourselves dealing with.
He also treated Sansa and his uncle Tyrion appallingly - the latter of which we should probably thank him for because it gifted us with this 10 minute-long loop of Tyrion slapping some manners into Joffrey to the tune of Led Zeppelin's Achilles Last Stand.
But still, he had Ros beaten and eventually killed, he had Ser Illyn Payne strip and beat Sansa in front of everyone, he also had Ser Illyn rip a man's tongue out, he put Ned's head on a pike for Sansa to see, threatened her family, threatened to make homosexuality punishable by death, and was generally just a terrible person.
That said, his death was perhaps one of the most gratifying in Thrones - just to watch his smug face turn blue like that, and see the pure shock on his face, because frankly, when you're that much of a tool you should expect for literally anyone you've met to be trying to off you.
RIP Joffrey, you were extraordinarily fun to hate, and easy to mock. Tommen ain't got nothing on you.
Rachel Bache: It's hard to know for sure with High Sparrow if he really believes he's the good guy or if he's just playing the game as much as anyone. Either way, this religious leader became pretty scary pretty fast. It's mainly Cersei's fault for giving High Sparrow's cult-like followers weapons, turning them into the faith militant.
Sure, she got what she deserved, but High Sparrow's treatment of her last season and the fact that he's got her son, King Tommen, wrapped around his finger makes him incredibly dangerous and makes you feel kind of sorry for Cersei, which isn't an emotion one should ever feel. High Sparrow is a master manipulator and he has the people of King's Landing on his side, but the newly appointed High Septon of the city definitely has his own ulterior motives in mind. The hint of a smirk when he knows he's played a better hand than his advisories says it all.
The thing that makes High Sparrow truly bad is that he holds himself as this self-righteous leader, but his actions of dishing out such cruel and unusual punishments so people can "atone" for what he deems to be "sins", puts him in a very murky, grey area. He's an unknown and could be the undoing of the Seven Kingdoms, which I'm sure in his mind would be a great thing. He really just needs to be taken out because I don't think I could stand one more of his religious speeches. He's not like Ramsay Bolton or King Joffrey where you almost love to hate them. With High Sparrow, you just hate him.
Joanna Hunkin: Granted, it may seem like a cop-out to choose Ramsay Bolton with his evil maleficence so fresh in our minds. But let's recap for a moment. This is a man who hunted humans for sport. Who fed a newborn baby to his hounds (not just any baby either but his own half-brother). A man who cut off another man's penis for his own amusement.
He raped, pillaged and tortured just about anyone who crossed his path. Oh, and he murdered his own father. Even by Game of Thrones' twisted standards, Ramsay Bolton is the baddest baddie of them all.
I just feel for Iwan Rheon - the actor who plays Ramsay. Interviewing him earlier this year, it was clear he wanted as little to do with Ramsay's legacy as possible. Unfortunately for him, it will be some time before anyone can look into those sparkling blue eyes and not see the glint of a psychopath.
Cameron McMillan: Technically the best villain is a character who has yet to utter a word of dialogue and we don't even know if he can speak. Two things working in the Night's King's favour: 1) He's still alive (or at least living in some form) and 2) He has potentially the most deadly army in the history of Westeros.
He has killed baby boys, massacred Wildings at Hardhome and was directly responsible for the deaths of Summer, Leaf, the Three-Eyed Raven and of course sweet Hodor.
We still don't really know his motive. Is his plan to turn everyone in Westeros into White Walkers? Then what? Will he just chill (pun certainly intended) on the Iron Throne?
All I know is that Joffrey, Ramsay and even Tywin wouldn't been able to match him.