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. They also seem to favor the use of Japanese-style swords (or katanas) as standard weapons, instead of the typical kunai that most shinobi wield; and, as a result, most Kumogakure ninjas seem to excel at swordsmanship. The village is located on a high mountain, and is literally hidden in the clouds. The Raikage lives in a large 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 at 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 the request of Hiashi's twin, Hizashi Hyuga, as well as the Hyuga clan and the Third Hokage, who didn't want 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 and Kirigakure, had two tailed beasts in its possession: the Two-Tailed Monster Cat in Yugito Nii, and the Eight-Tailed Giant Ox in Killer Bee. What makes this village unique is the fact that the villagers were outraged when both Yugito and Killer Bee were captured by Akatsuki, as most villages had shunned their Jinchuriki. Yugito and Killer Bee had a great deal of control over their tailed beasts, such that both were able to fully transform into their beasts. Due to the immense powers of releasing their beasts fully, despite retaining control of themselves, the Raikage forbade them from doing so (or at least Killer Bee).

Shortly after the Fifth Kazekage's abduction, Yugito was captured by Kakuzu and Hidan of Akatsuki, and she died after her tailed beast was extracted. After Killer Bee (the Raikage's brother) was captured, the village started dedicating its time to dealing with Akatsuki and saving Killer Bee.

Due to Sasuke Uchiha being the one who had kidnapped Killer Bee, Kumogakure felt that Konohagakure was responsible for sparing Sasuke's life even after his defection. As such, animosity between the two village rose, similar to when Hiashi Hyuga killed their Head Ninja.

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 that this rank is placed between Kage and Jōnin. It is unknown if this position is still applied.

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. Killer Bee, 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 Countries not to have a known Akatsuki representative.
 * So far, Kumogakure is the only village to portray noticeably dark-skinned people.
 * In real life, is the name of one of the nine schools of martial arts within the Bujinkan sphere of training - a real life ninja organization.
 * According to Onoki, Kumo is the only Hidden Village that hasn't begun to disarm in the times of peace.