Admittedly, not much has been revealed about Euron Greyjoy in the series yet, making his inclusion on this list questionable. However, several of things that he is either acknowledged or hinted at being responsible for paint the picture of a highly villainous individual. A shrewd manipulator, Euron is hated by his family and found himself banished from the Iron Islands after raping the wife of his brother Victarion. He returns with his ship and men, all of whose tongues he has removed, the day after the death of another of his brothers, Balon, the ruler of the Islands, lending credence to the belief that he was involved in his demise. At a Kingsmoot organised by his other brother, Aeron, who he is heavily implied to have sexually molested as a child, he becomes the new ruler of the islands, murdering several prominent individuals who object to his ascension. He then sends Victarion across the world to court Daenarys Targaryen, who he presumably seeks for nefarious purposes with the implication that he wishes for Victarion, the biggest threat to his rule, to die in the process. Euron will presumably play a larger role in the final two books as House Greyjoy becomes increasingly involved with the overlapping plots of the series, and his future actions are eagerly anticipated given how Martin has managed to create a monster out of the character in just a handful of mentions and appearances.