Kumogakure

is the hidden village of the Land of Lightning. As one of the five great ninja villages, Kumogakure has a Kage as its leader known as the Raikage. The ninja from this village seem to specialize in Lightning Release techniques. It is located on a high mountain, literally hidden in the clouds. The Raikage lives in a big building built into the tallest mountain.

Hyuga Incident
At one time, Kumogakure was at war with Konohagakure. However, on the day of Hinata Hyuga's third birthday, both villages signed a peace treaty. This treaty was soon revealed to be nothing more then a cover when the the Head Ninja of the time, who was in Konoha to sign the treaty, attempted to kidnap Hinata in order to obtain a Byakugan and its secrets. The Head Ninja was killed in his attempt by Hinata's father, Hiashi Hyuga.

Kumogakure denied all accusations and demanded the dead body of Hiashi as compensation for the death of their Head Ninja. At request of Hiashi's twin Hizashi Hyuga, the Hyuga clan and the Third Hokage, not wanting to lose the heir to the clan, decided to send Hizashi's body instead. This had another advantage, besides saving the life of the Hyūga heir; Hizashi's Cursed Seal would seal his Byakugan after his death, safeguarding its secrets. Although they are not allies, Kumogakure and Konohagakure seem to be on friendly terms now.

Five Kage Summit arc
Kumogakure, like Iwagakure, is unique for having had two tailed beasts in its possession: Yugito Nii and Kirābī. Equally unique is the fact that the village is outraged when both Yugito and Kirābī are captured by Akatsuki, as most villages had shunned their jinchuriki. After Kirābī (the Raikage's brother) is captured, the village starts dedicating its time to dealing with Akatsuki and saving Kirābī. Yugito and Kirābī had a great deal of control over their tailed beasts, such that Kirābī was able to fully transform into his beast.

Shinobi
The organization of Kumogakure's shinobi is slightly different from other villages. Besides the normal ranks of Kage > Jōnin > Chūnin > Genin, Kumogakure has an extra rank, that of. It seems this rank is placed between Kage and Jōnin. It is unknown if this position is still beeing aplied.

Yotsuki clan
Not much is known about the shinobi from Kumogakure. Besides being home to two Jinchūriki, Kumogakure is also home to the Yotsuki clan. Kirābī, the host of the Eight-Tailed Beast, and his older brother, the current Raikage, are possible members of this clan.

Trivia

 * Kumogakure is the only one of the Five Great Shinobi Nations not to have an Akatsuki representative.
 * So far, Kumogakure is the only village to portray noticeably dark-skinned people.
 * In real life, Kumogakure-ryū Ninpō, (literal meaning; "The Hidden in the Clouds School" is the name of one of the nine schools of martial arts within the Bujinkan sphere of training--a real life ninja organization.