In Masashi Kishimoto's long running Naruto series, there are only a few who can truly rival the power of the Nine Tailed Fox. Naruto may be centered around protagonist Naruto Uzumaki, but there is much more to the story itself than the title character himself.
Kurama a.k.a. The Nine Tailed Fox is first introduced in chapter 1 of the original Naruto manga, representing one faction of the powerful and ancient tailed beast creatures. Harboring great vengeance against the leaf village of Konoha, the Nine Tailed Fox would lay waste to the leaf village where it would find itself up against the current leader of the village the fourth hokage, Minato Namikaze. Following a lengthy battle, the beast would then be sealed inside the baby son of Minato and wife Kushina Uzumaki by Minato himself, with the two ultimately sacrificing themselves for their boy, Naruto, to live. Thanks to the Nine Tails, Naruto (who now bore fox like whiskers on his face) would be born into becoming shunned and alienated by most of the leaf village for the better half of his childhood.
Though Kurama remained trapped inside Naruto for the foreseeable future, the creature would end up gifting Naruto some of its powerful chakra in exchange for survival. The Nine Tailed Fox would become a key factor in an inexperienced Naruto arising the victor against some of his greatest early opponents including enemy turned close friend Gaara of the sand village, former leaf village student Orochimaru, and Haku the young servant to the deadly Assassin of the Mist, Zabuza Momochi.
As Naruto would grow and develop into much more of an experienced ninja in the manga's second half, the relationship between Kurama and Naruto would also develop. Rather than Kurama simply taking hold of Naruto for a short period and Naruto remaining in the driver's seat, the fox would begin to take over completely. Naruto no longer in control, thus strengthening the hold over Naruto's consciousness. This form would become dubbed as the Nine Tails Cloak. However, Naruto and the Nine Tailed Fox would eventually become more than just temporary bunk mates sharing the same body. Near the tail end of the series' climatic Fourth Shinobi World War, Naruto and Kurama would eventually find common ground, in which Naruto would gain complete control of Kurama's great power.
Given that the Nine Tails is nearly the strongest of the tailed beast creatures, Kurama comes equipped with equally powerful feats of strength, which are then passed on through Naruto. Aside from being a brute of a creature, the Nine Tailed Fox can detect chakra, emotions, and energy from great distances, withstand numerous ninja attacks, retain a great amount of chakra after exhausting its own, can create a powerful tailed beast ball, as well as produce destructive shock waves capable of destroying city blocks.
Throughout the entirety of both Part 1 and Part 2 of the series, Naruto has shown countless times that he is an extremely talented ninja, even without the power of the Nine Tailed Fox at his side. Though, it cannot be denied that the Nine Tailed Fox is the ultimate support system in Naruto's journey to becoming the greatest ninja throughout the land.