Jinchūriki

The, or hosts, exhibit extraordinary powers, and in some cases are stronger than their Tailed Beasts for the very fact that they are able to control their power.

In addition, if a Tailed Beast goes too long without a host, it can lose its intelligence and become nothing more than a giant animal.

Appearance
The hosts usually show some physical characteristics of the Tailed Beast within them (likewise Naruto's fox-like "whiskers" on his cheeks and Gaara's raccoon-like "rings" around his eyes) and the Tailed Beast's traits can become infused with the host's personality.

Personality
According to Akatsuki, the Jinchūriki tend to be lonely people who loathe humanity, which was proven true when the first two Tailed Beasts that were sealed by the organizaiton was done with almost little effort from their ninja villages. In fact, they were glad to be rid of their Jinchūriki. The Tailed Beasts are also very protective of their hosts for the sole reason: if the host dies, so does the demon inside. Likewise, if the Tailed Beast is removed from the host, the host would die.

Mental Affects
There is a theory that all Jinchūriki have some sort of effect on their mental well being. This stems from the known fact that Gaara was unable to sleep ever. In the Chunin Exam Arc, Gaara used the Feigning Sleep Technique to allow the Shukaku to take control, and it was explained that he was unable to ever sleep normally because of the Shukaku. This leads to the idea that all Jinchūriki have some kind of mental problem due to the fact that part of them is always fighting to keep their demon contained. For Gaara, this is manifest in the inability to sleep. Very little is known about most Jinchūriki. However, since Gaara's seal was weaker on purpose, it probably does not have that much of a heavy effect.

Sealing
So far, there are only two known methods to seal a Tailed Beast into a host. One was the Dead Demon Consuming Seal, which Minato Namikaze, the Fourth Hokage, used to seal the Nine-Tailed Demon Fox into Naruto, and the technique that Chiyo used to seal the One-Tailed Shukaku into Gaara. The only known technique to extract a Tailed Beast is the Akatsuki's Illusionary Dragon Nine Consuming Seals, a three day long jutsu that with the combined effort of all the Akatsuki members, forces the Tailed Beast out of its host and into a nine-eyed statue. The Akatsuki has so far captured seven Tailed Beasts.

Power
So far, all Jinchūriki have displayed enormous powers and abilities, though each ability depends on which beast they have sealed within them. All Jinchūriki so far have different fighting styles (i.e. Gaara controls sand, while Yugito controls fire). It is also implied that Jinchūriki that have full mastery over their Tailed Beasts can actually create and, in a sense, become the Tailed Beast, this has been shown in different versions by the four Jinchūrikis so far, however, Kira Hachi is the only one who can do this without a "catch" or condition, (i.e. Gaara could create the full Shukaku body, but couldn't access all its abilities without losing control, Yugito could create and control the body of the demon cat, but only in miniature form, and Naruto could only create a shell of the demon fox with its chakra, but resembles his actual beast in very little ways and Naruto also loses his mind in the process if he reaches his four-tailed state).

Known Jinchūriki
Gaara Yugito Nii Old Man Kira Hachi Naruto Uzumaki Sora (Pseudo-Jinchūriki) (Anime only)
 * Beast: One-Tailed Shukaku
 * Status: Captured and Extracted
 * Beast: Two-Tailed Demon Cat
 * Status: Captured and Extracted
 * Beast: Four-Tailed Beast
 * Status: Captured and Extracted
 * Beast: Eight-Tailed Beast
 * Status: Active
 * Beast: Nine-Tailed Demon Fox
 * Status: Active
 * Beast: Nine-Tailed Demon Fox's chakra
 * Status: Inactive Chakra absorbed by Naruto