The Eight-Tailed Giant Ox (八尾の巨牛, Hachibi no Kyogyū) is a demon ox sealed within Killer Bee of Kumogakure. It is described as an giant eight-tailed bipedal ox, with skin that looks roug in texture.
According to Madara Uchiha, the Eight-Tails came into being near the end of the waning days of the Sage of the Six Paths' life; to prevent its resurgence, the Sage split up the demon's chakra of the Ten-Tailed Beast into nine separate, monstrous constructs of living chakra, which would become known as the tailed beasts. The Eight-Tails eventually fell into the possession of Kumogakure and was sealed into Killer Bee.
Killer Bee and the Eight-Tails appear to be able to speak to each other in a much more relaxed state than Naruto Uzumaki and the Nine-Tailed Demon Fox. For example, when Naruto has a conversation with the Nine-Tails, the latter is in a cage with a special seal keeping it from taking over Naruto. As Killer Bee is one of the few people who has total control over his own tailed beast, he and the Eight-Tails can talk without such restraints, with Killer Bee even sitting on top of its muzzle. The Eight-Tails is shown to get easily annoyed with Killer Bee's crazy antics; however, that is somehow shown to be comical.
However, despite Eight-Tails' friendly relationship with Killer Bee, the Eight-Tails, like the other beasts, main goal is self preservation. For example, it was more than willing to be released and destroy Kisame Hoshigaki despite Sabu and Ponta being close by. However, behind the brutal appearance the Eight-Tails is shown to have a good analytical ability, as he told Killer Bee that if he left Ponta and Sabu and run in the opposite direction Kisame and the water will follow him and they (Sabu and Ponta) will be free
Activity inside Killer Bee Killer Bee and the Eight-Tails.Little is known about the Eight-Tails' strength so far. As the Eight-Tails' jinchūriki, Killer Bee can transform himself into the Eight-Tails and can access its high-level chakra without losing control. Killer Bee is one of the two jinchūriki who has been known to be able to fully control his tailed beast's powers, the other being Yagura. It has been shown to fire an attack similar to the Four-Tailed Fox Menacing Ball, but with much greater force. Killer Bee is also able to use the Eight-Tails to block his chakra to break illusions, even ones cast from a Mangekyō Sharingan. Killer Bee can also create ink because of the octopus nature that his tailed beast resembles.