There are five great ninja villages, each village has their own Kage. The Kage is the most powerful ninja in the village, and is not only the leader and protector of the village, but is used as an example of their village's might. Konohagakure's Kage is known as the "Hokage." Konohagakure have had a line of extremely powerful Hokages that have all been revered and engraved on the village's mountain on the eastern side of the city, much like Mt. Rushmore.
The First Hokage. Hashirama Senju was the leader of the Senju clan. After fighting against the Uchiha clan for so long, he eventually allied with them. Then together with his younger brother and Madara Uchiha, they formed Konohagakure. He taught the "Will of Fire" to the village and had a special blood-line ability that allowed him to create the forest surrounding the village. Some time later he and Madara had a falling out over the rights of leadership; he won and became the 1st Hokage. Their battle however was so great that it shaped what is now known as the "Valley of the End." The village engraved statues of Madara and Hashirama facing each other in the sides of the valley's waterfall. He would die of disease later on.
The Second Hokage Tobirama Senju was more passionate and enthusiastic compared to his calm and prudent older brother, the 1st Hokage. He had silver hair and specialized in water based jutsu; he was so powerful in fact that he didn't need a source of water, and prided himself on his superior combat skills. He taught Homura, Koharu, and Hiruzen. He also established Konoha's military might, police force, and academy. He ended up dying in battle to save his team after passing the mantle of Hokage to Hiruzen.
The Third Hokage. Hiruzen Sarutobi is the father of Asuma, and the grandfather of Konohamaru. He trained the Sannin and was called the "the Professor" because he knew every jutsu that originated in Konohagakure, including forbidden techniques. Growing older and weaker, he passed on the title of Hokage. But after the 4th Hokage's death, he resumed the title. When Orochimaru allied the Sunagakure and Otogakure villages to invade Konohagakure, he faced Orochimaru and sacrificed himself to force Orochimaru and his army to retreat.
The Fourth Hokage. Minato Namikaze was trained by Jiraiya, one of the Sannin. He was revered as a genius that only rarely appeared and became the Fourth Hokage after The Third Hokage retired. He trained Kakashi, Obito, and Rin. Shortly after becoming Hokage, the Kyuubi attacked Konohagakure and he sacrificed himself to seal the demon into his newborn son, Naruto, to save the village.
The Fifth Hokage. Tsunade is the granddaughter of The First Hokage and grandniece of The Second Hokage, she was trained by the The Third Hokage and became the Fifth Hokage after his death. She believes Naruto will one day be a Hokage. She is the greatest Medical ninja in the world and has taken Sakura and the niece of her deceased boyfriend, Shizune, as her apprentices. She has also given some medical training to Ino.
The Sixth Hokage. Danzo Shimura is very militaristic and logical, believing that emotion is destructive. Following Tsunade's coma, Danzo was selected as the new Hokage. He was originally Hiruzen's rival for the position of third Hokage, and created a sub division of the Anbu called "Root." He allowed himself to be the subject of experimentation in order to become more powerful and protect the village. Like the Hokages before him, he died trying to protect Konoha.