Hiruzen Sarutobi

was the. He was the student of the first two Hokages, Hashirama Senju and Tobirama Senju, and the teacher of Jiraiya, Tsunade, and Orochimaru.

Background
As a child, Hiruzen was a prodigy who truly stood out in talent. He and his former teammates, Homura Mitokado and Koharu Utatane, were students of Tobirama, who would eventually be chosen as the Second Hokage. Later in his life, he became the teacher of Jiraiya, Orochimaru, and Tsunade, who would go on to become known as the. In time, he became the father of Asuma Sarutobi and later the grandfather of Konohamaru Sarutobi.

While Orochimaru was his student, Hiruzen came to appreciate Orochimaru's natural talent and often told Jiraiya to be more like him. He also came to recognize an inner malice and a lust for power within Orochimaru, and tried to steer his student away from these personality traits. After taking the position of Hokage and occupying it for many years, Hiruzen started looking for a successor to the title. While he hoped to be able to give the position to Orochimaru, it became apparent that Orochimaru was only interested in the role of Hokage for the power it offered. As such, Hiruzen passed on the role of Hokage to one of Jiraiya's pupils, Minato Namikaze.

Soon after, Minato sacrificed his life to seal the Nine-Tailed Demon Fox within his newborn son, Naruto Uzumaki, forcing Hiruzen to reassume the role of Hokage. After reacquiring his title, Hiruzen began investigating a number of disappearances within Konoha. Upon reaching the source of the abductions, he found Orochimaru to be the one responsible. Having used those that he kidnapped as test subjects in his quest to gain immortality, Orochimaru allowed his former master a chance to kill him. Ultimately, Hiruzen was unable to bring himself to kill his former prodigy, allowing Orochimaru to escape.

In Part II, Hiruzen is revealed to have been one of four Konoha elders involved in the massacre of the Uchiha clan. Although he tried to find a peaceful alternative, his former rival for the position of the Third Hokage, Danzo, won out. Itachi Uchiha was ordered to wipe out the Uchiha, though when he proved unable to kill his brother Sasuke, Hiruzen promised to keep Sasuke safe. It is also revealed that he knew Naruto was the Fourth Hokage's son the entire time and kept it a secret from those who didn't know, to protect Naruto from trouble.

Personality
Due to the long life he has lived, Hiruzen served as a source of wisdom for much of the series, passing on the things he had learned to the next generation. As Hokage, he had also acquired a habit of attempting to end things peacefully, and did what he could to avoid bloodshed amongst his allies and his enemies. At the series' start, Hiruzen was one of the few people who saw Naruto as more than the container of the demon fox, and as such became someone that Naruto truly admired, even thinking of Hiruzen as a grandfather-figure.

Despite his standing as Hokage, he seemed to have had some sense of lecherousness in him as he spent much of his free time talking to young girls. When Jiraiya was still his student, he offered to help Jiraiya test the jutsu that would allow the user to spy on naked women unnoticed. Even Jiraiya, in this instance, noted his sensei's perverted qualities. He also fell victim to Naruto's Sexy Technique on more than one occasion.

Invasion of Konoha arc
When the invasion began, Hiruzen was forced to do battle with Orochimaru, who infiltrated the village and planned Konoha's destruction just so he could kill Hiruzen and kidnap Sasuke Uchiha. Soon after the battle began, Orochimaru resurrects Hashirama and Tobirama, so that Hiruzen can feel the enjoyment of fighting his former masters. In his old age, Hiruzen was unable to be much of a match for the two Hokage, and was further inhibited by his desire to not hurt either. Orochimaru's presence also impeded Hiruzen's fight, as seeing just how monstrous his treasured student had become broke his heart. Although he used his summon, Enma, to help him in battle, Hiruzen was unable to defeat the two Hokage, as any damage that was done was simply regenerated.

Having no other choice, Hiruzen used a combination of shadow clones and the Dead Demon Consuming Seal to seal away the souls of his former masters. As he bid a heartfelt goodbye to his teachers, he turned his attention to Orochimaru. Charging at Orochimaru and throwing aside his former pupil's Kusanagi, Hiruzen attempted to seal Orochimaru's soul as well. Sensing what Hiruzen was trying to do, Orochimaru called his Kusanagi to him, stabbing Hiruzen in the back.

Despite the fatal injury, Hiruzen continued to try to remove Orochimaru's soul, unconcerned with the sword in his back due to death being guaranteed as a result of using the Dead Demon Consuming Seal. After an hour passes, Hiruzen came to terms with the fact that he was too old and weak to completely remove Orochimaru's soul. Doing what little he could and hoping to rectify his mistake of allowing Orochimaru to escape years earlier, Hiruzen sealed Orochimaru's arms to ensure that he would never again be able to use jutsu, a punishment for Orochimaru's obsession with power. As Orochimaru began to curse his former master for what he had done, Hiruzen bid Orochimaru farewell and hoped that they would meet again. Knowing that the village was saved and seeing Orochimaru as the boy he once was, Hiruzen died with a smile on his face.

Abilities
Hiruzen was unarguably one of the most powerful shinobi in history. He has even been called the most powerful Hokage. Enma commented on his battle with Orochimaru, saying that it was "miserable" compared to his prime even though he had clearly been able to withstand Orochimaru and two former Hokage. He was also the longest living and longest reigning Hokage, and apparently had an undefeated streak, having defeated all foes that came before him until he sacrificed himself in order to stop Orochimaru.

Hiruzen was called due to his mastery of all forms of shinobi combat and his vast knowledge of jutsu, purportedly knowing all the techniques within Konoha. The first technique he was seen using is the Telescope Technique which allowed him to observe others through his crystal ball over long distances. With Roof Tile Shuriken, he could launch nearby tiles at an opponent with varying intensities, and by throwing a single shuriken at an opponent he could replicate it to surround the opponent through Shuriken Shadow Clone Technique.

The more battle-oriented techniques he was seen using primarily consist of elemental attacks, as he had an affinity for fire and earth. Fire Release: Fire Dragon Flame Missile allowed him to exhale a stream of fire from his mouth. Earth Release: Earth Flow River created a river of mud beneath the opponent to throw them off balance, and he could use the mud with Earth Release: Earth Dragon Bullet, which creates a dragon's head that launches mud balls at an opponent. He had also shown to be adept in elemental combo attacks as seen when he ignited the mud ball projectiles with Fire Release: Fire Dragon Flame Missile. Earth Release: Earth Style Wall allowed Hiruzen to spit a stream of mud that solidifies into a protective shield.

Orochimaru shows some surprise that he didn't use the Shadow Clone Technique during their battle. An ANBU agent watching the battle scene from nearby mentions that Hiruzen's chakra levels have dropped to a point where he can't use it as much. While this might contradict the large amount of techniques he used in his battle with Orochimaru, it could also show his great chakra control, needing only the minimum amount of chakra to use each technique.

Hiruzen also had a personal summon: Enma, the Monkey King. Enma could turn into a near diamond-hard staff which could alter its length and width at will. This staff was Hiruzen's weapon of choice, and he showed great proficiency in wielding it.

Trivia

 * His name, inspired by Sarutobi Sasuke, means "jumping like a monkey", further supported by his Summoning Technique which summons Enma. Tobirama also nicknamed him.
 * Many aspects of his character are borrowed from the Chinese literature classic Journey to the West. Hiruzen's summon, Enma, bears a very strong resemblance to, the protagonist of the novel, and Hiruzen's chosen weapon is identical to the Monkey King's magical staff.
 * During his battle with Orochimaru, maybe as a premonition to his death, Hiruzen's likeness on the Hokage Monument cracked across the face. While the crack was fairly prominent due to its size, it didn't always show up in the anime due either to a bad angle or a mistake by the animators.
 * Hiruzen was taught by the First and the Second Hokage. Hiruzen was once Jiraiya's teacher; Jiraiya later became Minato Namikaze's teacher, Minato taught Kakashi Hatake, and Kakashi taught Naruto Uzumaki. In addition, Naruto has also taught Konohamaru techniques like the Sexy Technique and the Rasengan.
 * Masashi Kishimoto originally planned for Hiruzen to be a dog, but eventually dumped the idea for being "too weird".

Quotes

 * "He has combined Shadow Cloning with his own invention, the Sexy Jutsu. What a foolish ninja technique...and he could probably get me with it, too."
 * (His last words before his death) "When the tree leaves dance, one shall find flames. The fire's shadow will illuminate the village, and once again, tree leaves shall bud anew."