A fictional group of fictional humanoid creatures known as 'Nobodies' within the video game of Kingdom Hearts. They are beings without hearts, and have banded together in an attempt to get their hearts back. Each wear a black trenchcoat with a hood, and have a signature weapon and element. Whether they are 'evil' or not is up for debate. They lack hearts, and thus are incapable of feeling any emotions such as remorse.
Also, they are probably the only 'villains' (for lack of a better term) in history to have a bigger fanbase than the main characters. They're names are all anograms of their original names with an 'x' added.
Organization XIII is awesome.
A group of 13 Nobodies who retained human form and are fighting to get their hearts back. They are from the popular Kingdom Hearts series. However, they are also the only villans who have a larger fan following than the main characters. Many members (such as Axel and Roxas) are paired together in yaoi relationships, canon or not. Mostly not. They were taken down member by member by Sora, the main character (who wield a giant KEY), and his many Disney and Final Fantasy friends. It is also interesting to note that Organization XIII only has one female member (Larxene) because Xion was not a true member and the rest are male.
Axel, Roxas, Demyx, and Xigbar are all Nobodies who are members of Organization XIII.