Naruto was born on October 10 to an unknown couple in the fictional village of Konoha. When Naruto was a newborn infant, a powerful nine-tailed demon fox attacked his village. In order to save the village from destruction, the demon fox was sealed in Naruto’s body by the Fourth Hokage, leader of the village at the time of the attack.
Despite the Fourth Hokage’s wish that Naruto be veiwed as a hero who was forced to encase the demon, the villagers of Konoha harbored a fierce hatred for him, some believing that Naruto and the demon were a single entity. However, nobody told Naruto about what his body harbored until he was twelve years old, leaving him confused for most of his childhood about why the villagers of Konoha treated him with malice.
Naruto is seen to be a prankster and a loner, living by himself in a small apartment. Even though Naruto was treated as an outsider, he was befriended by his compassionate ninja instructor named Iruka Umino. Although Iruka’s own parents perished during the battle with the demon fox, he refused to view Naruto as the cause of their deaths. Instead, Iruka attached himself to Naruto, because he too was once an outcast and desired recognition. Naruto is obsereved to be deeply moved by Iruka’s kindness, and confidence in him. As a result, Naruto is seen to value Iruka more as an older brother or even a father, than an instructor.
As the host of the demon fox, both Naruto’s body and mind (occasionally) are influenced by it. Physically, Naruto has some of the demon fox’s characteristics, such as whisker-like marks on his cheeks and larger canines than normal. His eyes are also somewhat slitted like a fox. He also has increased stamina and healing ability, which allows him to recover from major injuries within a day and minor injuries within a few seconds. Mentally, Naruto remains largely unaffected, save for a few animalistic traits that slip through, such as his occasional tendency to leap between trees on all fours. Since the demon fox was sealed inside Naruto at birth, it is unclear just what parts of his personality it has had an effect on; however, it could explain Naruto’s devilish side for pulling pranks to gain attention, as well as his stubbornness to never back down from a challenge. These traits become more pronounced as he draws upon the demon fox’s chakra.
The kitsune (狐) is a well-known character in Japanese folklore, and the influence behind not only the demon fox but many other reincarnations in modern Japanese culture. It likes to play tricks and pranks on people, and on occasions transforms itself into a beautiful woman and seduces a man. Also, Kitsune are known to keep their promises, a trait Naruto has, as his "ninja way" is to "never go back on [his] word." It should also be noted that every time Naruto loses control and is overwhelmed by the demon fox’s chakra, he seemingly gains another "tail" of chakra. The chakra that surrounds his body and its "tail" act as a sort of shield most of the time, until it gets to as high as four "tails". This stems from the belief that the more tails a kitsune has, the more powerful it is, with nine tails usually being the limit.
The demon fox’s chakra usually comes to Naruto during life threatening or other stressful situations, given to him by the fox itself to ensure its survival. Naruto eventually learns to contact the fox and demand some of its chakra, which it seems to comply to out of amusement. The reason Naruto is able to access its chakra is because of the unique way in which it was sealed. Though the fox remains trapped within Naruto, its chakra can leak out through the seal and mix with Naruto’s. The fox’s near-limitless supply of chakra becomes an invaluable weapon for Naruto, often turning the tide of a difficult battle in his favor. Beyond that, the fox’s chakra seems to increase in intensity with time. Several external methods can be used to suppress it once this occurs, such as Jiraiya’s sealing talisman or Yamato’s sealing techniques.
This tremendous power is not without its disadvantages, however. When he first accesses it, Naruto is unable to retain control when using the demon fox’s chakra, allowing its innate rage and anger to take over his personality. Over time, Naruto gains more control over the demon fox, allowing him to retain his personality while using its chakra. However, his degree of control is determined by the amount of chakra he draws upon and his emotional state. As he becomes more emotional and draws on more of the demon fox’s chakra, his own personality is gradually supplanted by the demon fox’s. When Naruto completely loses control and grows four chakra "tails" the demon fox’s personality takes control. His body is completely covered in the fox’s chakra to a point where he looks like a miniature demon fox as his body acts like a skeleton for it. Because his body is completely covered in the fox’s chakra, it is constantly destroying and healing his skin, therefore shortening his lifespan.