Sarutobi Hiruzen, also known as Sandaime Hokage, is the Third Hokage of the Hidden Leaf Village. Hiruzen is 68 years old and this is his second time to be Hokage. He retired once, so that Namikaze Minato would be able to get the title, but when the Fourth died in his fight with Kyuubi, he once again became the Hokage. He was the instructor of the three Sannin - Orochimaru, Jiraiya and Tsunade, the most noted ninja team of their era, but eventually all three 'left' Konoha to experience life. He is the first known to have done the bell training that we see Team 7 doing. To most of the villagers he is very warm and paternal figure that mainly protects the villagers in a very kind and gentle way. Through his wisdom and strength as a leader, Konoha continued to flourish while he was the Hokage. His reputation for knowing all the jutsus from the village of Konoha has earned him the name "The Professor".
Eventually, at the chuunin exam that Naruto participated in, Orochimaru made an alliance with the Sand Village to attack Konoha and he engaged Hiruzen in a one on one battle. Orochimaru summoned the two previous Hokages, Hashirama and Tobirama, to fight him and the outcome was that Hiruzen died, sealing Orochimaru's arms and disabling him from doing any more jutsus. So he, like the Fourth Hokage, makes the ultimate sacrifice and forfeits his life to protect the village.