Gyuki is an ushi-oni with four long horns on its head, similar to that of a Jacob sheep. As a tailed beast, it is extremely massive, dwarfing entire forests and towers over large rock formations and buildings and matching the Giant Squid in size. The lower left part of its horns was permanently sliced off in a battle with Ay, and the right horns were destroyed by its own point-blank Tailed Beast Ball when fighting the Ten-Tails. It also has straight teeth, one of which was blown off during the point-blank Tailed Beast Bomb. Following the Fourth Shinobi World War, it grew another tooth. Gyuki also has a muscular upper-body structure, with a hunched back similar to an American bison, arms with spiked protrusions on the elbows, and hands with opposable thumbs like that of a human. Instead of hind-legs, its lower half consists of its eight tails, which resemble the cephalopod arms of an octopus. These tails will grow back in the event they are sliced off.
Gyuki is characterized as a tough, stern and serious individual. It uses "ore" when referring to itself and often speaks in a somewhat rude dialect. Gyuki was also shown to have a good analytical ability, as it told Killer Bee that if he left Ponta and Sabu and ran away from them, Kisame Hoshigaki and his water dome would follow him and they (Sabu and Ponta) would be freed. With regards to its relationship with the other tailed beasts, Gyuki mentioned that it and its brethren disliked Kurama for its habit of ranking their strength based on their number of tails. However, it insisted that was no reason for not helping Naruto Uzumaki to control Kurama's power, hinting a benevolent side. Since then, both Gyuki and B have taken a liking to Naruto.
In the past, Gyuki was infamous in the Hidden Cloud for being wild and violent, as it went on countless rampages whenever its former jinchuriki would lose control of it. This was most likely due to its hatred against humans for oppressing and sealing it away many times. Gyuki maintained this behavior until it was sealed within Bee, who would later change it after he bested it in one-on-one combat. Since then, Gyuki's personality has become much more relaxed, becoming close friends with Bee; even allowing him to sit on top of its muzzle while talking to it leisurely. However, Bee tends to annoy Gyuki to comical effect, as its no-nonsense demeanor often contrasts with B's tendency to goof off whenever he likes, adding fuel to Gyuki's irritation to its vessel.
As a result, Gyuki is not above bad-mouthing Bee and is also known to reprimand him in serious occasions. This was seen when Gyuki criticized Bee for rapping in his fight with Kisame when he should have been completely focused on their opponent, and later when it comically bumped Bee in the head when the latter started to mention in a perverted manner how Yugito's chakra receivers were embedded in her left breast and when Obito disappeared B was wondering if he escaped only for Gyuki to tell Bee to find him. This somewhat contradicts the original point of having a jinchuriki which is to control a tailed beast, but Gyuki seems to be more of the one in control than Bee. Because of this, Gyuki appears to be much more noteworthy than B as far as responsibility is concerned. Nonetheless, Gyuki formed a very strong bond with Bee, as even after being extracted from its jinchuriki, the tailed beast severed a piece of itself to help sustain Bee's life.
Gyūki's relationship with its Bee's predecessor Blue Bee was unknown in the manga, other than the fact it would pounce on the "hole" in Blue Bee's heart and assume control over him. In the Naruto anime, however, Gyuki stated it had high hopes for Blue Bee, indicating it bore no ill will towards its former host.
Tremendous Chakra Power: As a tailed beast, Gyuki possesses a massive supply of powerful chakra and can share it with others. It can replenish its enormous reserves in a short amount of time even after an entire day's usage. Should the need arise, it can disturb Bee's chakra with its own to dispel even genjutsu cast from a Mangekyo Sharingan. If Gyuki's tentacles are severed, they can be used as a medium for its chakra, such as creating a clone of its host, or transferring chakra to said host should the beast be extracted. A Hidden Cloud ninja who ate one of the tentacles in an attempt to gain jinchuriki-like powers died from the chakra instead.