Kurama

Kurama aka. Kyuubi is the Nine-tailed Fox that is curretly sealed in Naruto and is the strongest of the Nine-tailed beasts.

Having treated as volatile but soulless tools like other Tailed Beasts, it developed into bitter bijuu whom despised humans for what they did. Why it eventually having such hatred was aside its own infamous reputation as the ancient natural disaster that appearing suddenly out of nowhere to attack areas that have been breeding grounds for the darkest aspects of human nature, its innocence has selfishly ruined by Madara through his Sharingan that turned it into his slave. Even after regained it's sense, the damage that Madara done by using it proved so great that it resulting a superstition among humans that Kurama was proposed as amalgamation of humanity's negative emotions sustained by enormous ounce of chakra (superstition which it ironically taking such belief itself out of bitterness). However, after witnessing Naruto's determination to save it's fellow Tailed Beasts, it eventually redeemed himself and thus, proved the said superstition as hoax.

Personality
Kurama is known being cynical, arrogant, and shrewd individual, along with a somewhat twisted sense of humour. It uses "washi" (ワシ) when referring to itself, which is generally used by older men. Its arrogance was shown on his belief where the strongest tailed beast supposedly the one with more numerous tails, which is disapproved by Shukaku. But its arrogance does have it's limits though, as it claimed that it was unlikely to it to stand a chance against Ten-Tailed Beast alone by itself. However, it does easily get annoyed when Naruto uses a power other than its own, claiming its jinchūriki needs no other power than its own. It is also shown that Kurama deeply cares about Hagoromo Ōtsutsuki, viewing him with great respect and even shed tears after the Sage had imparted his final words to them.

Perhaps as results of humanity's negative treatment on him, he became bitter as seen in the beginning of the series,  even going as far as proclaiming itself to be the living embodiment of hatred like what everyone believed. Ever since his imprisonment, it will do whatever it takes to free: Triest to kill Naruto's parents before sealed completely inside their child out of desperation (though Obito, whom mastermind it's rampage in Konoha freedom mostly blamed for this and Kurama more like the scapegoat instead the killer) and manipulate Naruto for too dependant with it's chakra instead his. This ultimately backfires when Naruto ultimately stripped most of his chakra in the end, and also locked him with improved seal. However, in spite of his manipulation, he does have respect for Naruto and his determination. He also once warned the immense hatred inside Sasuke (though was only a ruse that backfires once again and Naruto retaliates by saying that he will do something that will change it someday). After having witnessed all of the challenges and endeavours Naruto had in his life, and Naruto succesfully freed Son Goku from Obito's control, it finally became convinced of Naruto's word and offered to meld its chakra with his as a coalition, to which Naruto then removed the seal that restrained it and happily acknowledged the fox as his team-mate and a member of Konoha.

All in all, two things are clear about Kurama: First, Kurama is merely a bitter and symphatetic bijuu who wished to treated as person instead of tool as well as capable to perform good deeds as he proved through its jinchuuriki friend Naruto, and second, the belief where it being composed of malevolence and chakra that merges into nine-tailed fox-like kaiju is hoax and superstitions made by those who despised him in the past stemmed from his reputation and power.