The Fourth Hokage and also known as Konoha's "Yellow Flash" with his blonde, spikey hair. Yondaime is alluded to be the greatest ninja that Konoha has ever produced. Yondaime was a respected and popular Hokage and is also seen to have a gentle and wise spirit.
Yondaime was mentored by Jiraiya, one of the Legendary Sannin, along with the two teammates who have yet to be named. After becoming a Jounin, Yondaime became sensei for a team consisting of Kakashi, Obito, and Rin. Yondaime is feared by the opposition in battle and, during war time, ninjas are told to "flee on sight" if they're ever misfortunate enough to meet the "Yellow Flash."
Not much else is known about him, other than the fact that he saved Konoha from the Nine-Tails Fox thirteen years ago. In order to do this, Yondaime was forced to sacrifice himself using the Demonic Soul Seal technique, and he then sealed the Kyubi's soul into Naruto. It is not known how Yondaime sealed the Kyubi in Naruto, and it is also unknown how Yondaime and Naruto are connected, whether it be family or otherwise.
Not much has been seen of Yondaime in battle. The one technique that was seen, the Body Flicker Technique, consists of placing a seal or marker onto an opponent. This allows Yondaime to instantaneously move from his spot to behind his opponent, literally in a "flash." Although no one has Yondaime use it, it is also known that it took him three years to develop and perfect the Rasengan. Through the battles that we have seen though, we gather that he is an immensely powerful as he approaches incredible odds and dispatches them to the amazement of his comrades. He strikes fear into his opponents with his speed.
His strength though is matched with his desire for the village and the people in it. When he is tutoring Kakashi's team, he is gentle yet firm with them even when they disobey his orders. He attempts to reconcile differences and make peace within his team so that they will be able to act with unity and not divisiveness. And eventually he does make the ultimate sacrifice with for his village in using the technique that demands his own life. So he like his predecessor sacrifice their life for the protection of the village.