(Spoiler Alert if you haven't read the books.)
- Ramsay Snow (aka Ramsay Bolton)
Ramsay is a sadist; he is cruel, savage and wild, taking delight in torturing others. He is quite fond of the old Bolton custom of flaying their enemies alive. He is a capable manipulator and possesses a low cold cunning. He is particularly good at thinking on his feet, though less savvy when it comes to long-term consequences and intricate politics. He openly enjoys abusive practices such as having young women stripped naked and released into the Bolton forests, before hunting them with a pack of feral dogs. He gives a quick death to women who give him good sport (after raping them first), then flays their corpses. The women who do not give him good sport are raped and then flayed alive. The skins of his kills are brought back with him to the Dreadfort as gruesome trophies. The bodies of the woman are fed to his dogs.
- Olenna Redwyne (aka The Queen of Thorns)
Olenna walks with a cane and claims to be near deaf, but both might be part of her feigning to be more frail than she actually is. She plots, sabotages, starts rumors, and generally controls everyone around her. She is responsible for killing King Joffrey.
- Viserys Targaryen (aka The Beggar King)
Viserys is ambitious, and cruel, prone to mood swings and fits of violence, impatient, cowardly, delusional and blind to reality. He sees himself as a rightful King due instant respect and admiration and takes anything less as an insult. He beats his little sister, Daenerys, and attempts to steal her virginity the night before her wedding. He would frequently warn her not to "wake the dragon" and incite his anger.
- Daenerys Targaryen (aka Dany, Daenerys Stormborn)
In her youth, Dany was a meek, timid girl with little confidence or self-esteem. She knew no life other than one of exile, dependent and in constant fear of her brother Viserys. Her marriage to Khal Drogo was a turning point for her, it allowed her to begin to achieve independence from her abusive brother, and she emerged from the experience as a strong, confident, courageous woman. She seems to have inherited a natural gift for leadership as her birthright. It was often said that the Targaryen kings tended to be either madmen or brilliant rulers, and she is constantly battling herself internally, between thoughts of giving in to her dark side, or remaining a virtuous leader. Her primary weakness as a ruler is her youth and relative inexperience; however, she has a keen intellect and learns quickly from her mistakes. Despite her strong moral compass, however, she is capable of dealing ruthlessly with her enemies.
- Petyr Baelish (aka Littlefinger)
Petyr was born to a small and insignificant house, spending most of his adult life trying to rise above his lowly birthright and become something greater, craving for power and status. He possesses considerable skill in commerce and coin, and is a master of court intrigue, his brilliance matched only by his ambition and his gift for political improvisation. He is often underestimated by many high lords due to his low birth (a mistake that often comes back to haunt those who make this assessment). He has spies everywhere, and advocates in the assassination of Daenerys Targaryen. He shoves Lysa Tully out the Moon Door to her death.
- The Faceless Men
Followers of Him of Many Faces consider death to be part of the natural order of things and a merciful end to suffering.
For a price, the guild will agree to kill anyone in the world, considering this contract to be a sacrament of their god. The price is always high or dear, but within the means of the person if they are willing to make the sacrifice. The cost of their services depends on the prominence and security of the target. The price could be someone's income or a child.
An elite group of followers within the House, called the Faceless Men, are trained to perform this task. Faceless Men are occasionally women. Only rarely would they train a child. They are trained to use all their senses to root out deception and create their disguises, seemingly possessing magical abilities that allow them to change their appearance at will. Part of their training includes discarding their true identity in a nihilistic way, thinking of themselves as "no one".
The Faceless Men reconvene at the House of Black and White, the "temple" of the Many-Faced God, where they discuss the potential jobs for the month and dole these contract assassinations out through a round table. They use a variety of methods to kill their targets, including a poison called the strangler.
They also cure the faces of the dead who come to die in their sanctuary, hanging these on the wall as macabre masks for use in their disguises during assassination contracts. These are more than masks, however, and the wearer assumes the true appearance when applied using a tribute of one's own blood to moisten the application. In this way, the Faceless Men are using tools as part of their disguise, rather than a reliance on glamours or outright magic for disguises, like Melisandre.
The assassination technique by a Faceless Man must not be haphazard, killing only the intended target. Their fee is for a precise killing, in many cases looking like an accident, rather than an outright murder.
(Feel free to add more.)