Jinchūriki

The Jinchūriki, 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 thus making it weaker.

Appearance
The hosts usually show some physical characteristics of the Tailed Beast within them (likewise Naruto's foxlike "whiskers" on his cheeks and Gaara's raccoonlike "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.

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 Akatuski members, forces the Tailed Beast out of its host and into a nine-eyed statue. The Akatuski has so far captured seven Tailed Beasts.