Hatake Kakashi, or "Copy Ninja Kakashi" is 's, 's and 's sensei. Usually discrete by nature about everything including himself, it seems that he wants to keep who he really is a secret to others and he always keeps his lower face hiddenby a mask. Kakashi also has a reputation of being a severe and demanding teacher, having returned all of his previous students before Naruto and his teammates to the academy. He said that all the others were brainless kids that didn't know what teamwork is and that they only obeyed to what they were told to do, teamwork seems to be very important to Kakashi. But, even though he seems to be cold sometimes, Kakashi loves his student and care for them enough to protect them at all costs, even his life, and he demonstrated that with Orochimaru and Zabuza.
Kakashi is quick thinking and seems to always be one step ahead of everyone and almost always knows how to act accordingly, even though he's always late to every appointment he has, important, or not! Moreover, Kakashi always has an ethically questionable book on him from the "Come Come Paradise" trilogy, and he even reads it in his first combat with his students which, of course insulted Naruto and got him into some "trouble"!
Like a lot of characters in Naruto, Kakashi's past is a tragic one, dirtied with the death of many friends and relatives. First, his father, Hatake Sakumo (AKA: White Fang), was disgraced after he abandoned a mission to save his friends, but because of that, Konoha suffered great losses and the village and his companions blamed the White Fang for that, thus, making him weak of mind and body because of the guilt he felt for his failure, and ultimately leading him to suicide. And for that reason, Kakashi became very strict about rules and regulations until 13 years ago...
It is known that Kakashi became a jounin 13 years ago (from where the manga currently is), at age 16. At the time he was training under Konoha's future fourth Hokage, Yellow Flash. He was in a three man team with Uchiha Obito, whom he never got along very well because Obito never obeyed rules and regulations, and Rin. At the time, there was great turmoil between the great countries and Konoha was deeply involved in what was to be called: The Third Secret World War. All four ninja were involved in a sabotage mission during the war and went to Rock Country. During the mission, the future fourth had to separate from Kakashi and the rest, so Kakashi was given charge of Obito and Rin.
Unfortunatly, Rin was captured by enemy ninjas and Obito went to rescue her without Kakashi who was still stuck up with his rules and regulations (he wanted to resume the mission without her). Obito had found Rin, but was about to be killed when Kakahi, who finally understood that teamwork and companionship was more important than rules, stepped in and injured the rock ninja. After some battle Kakashi injured his left eye and they were both about to be killed when he was helped by Obito who had his Sharingan awakened and killed the camouflaged enemy. The enemy's companion that was cornered used a Doton jutsu to make some rocks fall on Kakashi's team. Rin got out of the way but Kakashi was hit by a big rock on his blind side and fell to the ground, in an ultimate act of courage, Obito pushed Kakashi out of the way, therefore, saving him. Half crushed under the rocks, slowly dying, Obito's last gift to Kakashi was his Sharingan in his left eye, that was transplanted by Rin into Kakashi, making Kakashi what he is today, always being late and privileging teamwork to carry on Obito's legacy.
Afterwards Kakashi became an ANBU team member for a number of years, his only known mission was a rescue mission to save Snow Country's princess. But, judging from what we have seen in that part, we can deduce that Kakashi has been a normal jounin only for a few years.
Kakashi's fighting technique is complex and complete. First of all, Kakashi is quick thinking and has a developed sense of smell, thus making him very receptive to dangers surrounding him. He's also an excellent scout because of his great sense of smell and his ability to summon dogs. Kakashi, more than Sasuke, has learned how to use his Sharingan to the best of it's capacity. He knows the genjutsu that are related to the Sharingan and he can easily confuse powerful enemies like Zabuza with it. Moreover, Kakashi's favorite use of the Sharingan is it's copying ability. It is said that Kakashi has copied more than a thousand techniques with it, making Kakashi's arrays of techniques an exceptionally wide one.
Finally, Kakashi can even foresee the enemies moves with his left eye, making him even more shrewd. Aside from his Sharingan, Kakashi devised a formidable and powerful jutsu named Chidori/Raikiri. With this jutsu, Kakshi can virtually pierce everything from rock to flesh. Adding to this great array of ninjutsu, Kakashi is a formidable taijutsu user, and proves to be a strong enemy to even taijutsu users like Gai and can easily hold his own in close combat, like he does against Zabuza. The son of the once respected White Fang can wisely use genjutsu to his advantage in combat, and he can use a lot of them, making him a dangerous adversary even when the enemy is in hiding or keeping a distance.
After two and a half years, Naruto and Jiraiya return to the village earlier than expected because of the impatience of Akatsuki at capturing Naruto for his Kyubi no Yoko (Nine-Tails Fox Demon). Kakashi forms a team with Naruto and Sakura again. However, the relationship between the three is no longer teacher and students, but equal teammates.
Kakashi decides to test Naruto and Sakura's skills with another bell exercise, identical to the one they underwent with Sasuke when they first met Kakashi. The exercise reveals that Naruto and Sakura's skills and abilities had improved over the years, though he is still able to keep the bells from them. However, Naruto and Sakura manage to finally retrieve the two bells by preying upon Kakashi's addiction to the "Icha Icha" ("Make-out") series of books written by Jiraiya. During the test, they try to spoil the ending of the latest volume, "Icha Icha Tactics" , which Naruto gave to Kakashi. Kakashi is forced to both cover his ears and close his eyes, since he could read their lip movements with his Sharingan.
Yamato has informed Kakashi of all that has occurred during the Grass Country mission. When Naruto, Sakura, and Sai visits him at the hospital, he informs them of a new training technique he created that will help them improve their strength and be able to compete with Sasuke. Specifically it was designed for Naruto. After this training, Kakashi says that Naruto's strength might surpass his own. This training involves creating his own ultimate jutsu, one that can even surpass Rasengan (or even Hiraishin). He also stated that due to this, Naruto wouldn't be super powerful within a few days like some protagonist from a novel (this likely refers to Shonen manga in general, parodying it in that the main characters frequently gain enormous amounts of power easily and in a short period of time). Before he can finish, Ino and the rest of her group come in and interrupt during the conversation so they weren't able to go on but Kakashi says they will continue later. Kakashi is also about to discuss an important matter with Asuma. Then Kurenai interrupts them, and Asuma leaves with her.
Later, when Kakashi leaves the hospital, he finally begins to explain to Naruto how he will train him to complete a new more powerful jutsu. It involves two techniques. The first technique involves 'altering the nature' of one's chakra. The second technique involves 'altering the shape' of one's chakra. He explains that the Rasengan is an example of altering the shape of chakra, and that his Chidori is an example of 'altering the nature' of chakra (in this case creating an electric current). In order for Naruto to create his new jutsu he must
learn the technique of altering his chakra's nature.
Kakashi explains to Naruto that the method to speed up his training involves the use of shadow clones. Kakashi explains that because they are actual clones, Naruto will remember everything the clones do once they disperse. Kakashi then helps Naruto discover the element Naruto's chakra is based on using a special kind of paper that reacts to chakra. Handling the paper as an example, Kakashi makes it crumble, showing his affinity to lightning. When Naruto channels his chakra into the paper, it splits, indicating that he has an affinity for wind. With that, they begin training to manipulate that element. Kakashi explains to Naruto that the wind element is considered the strongest type for battle.
Kakashi begins the training by having Naruto and each of his clones hold a single leaf in their hands, and try to split the leaf with just their chakra. After some effort, only one of the 1000 clones manages to split the leaf. After seeing this, however, Kakashi remarks that this training may go faster than he thought. He also comments that Naruto is learning how to use his clones effectively, after he uses one to pick up some tips from Asuma Sarutobi, another wind-element user. He then tells Naruto to go and cut the newly created waterfall, using Yamato's wood as a floor to stand on. Once Naruto splits the whole waterfall (rather quickly according to Kakashi) Kakashi takes Naruto to get some Ramen after Naruto passes out. When finishing his meal, Kakashi states that he has something very important to show Naruto.