Fourth Hokage

The forth Hokage was originally was the replacement of the third. He was one of the best ninjas to have ever lived. His nickname is the Yellow Flash because of his ability to use shunshin(body flicker) no jutsu. He was able to seal the nine tails (Kyuubi) in Naruto at cost of his life. He used to be a student of the current Sennin Jiraiya. And also was the teacher of Kakashi. He also created the Rasengan that Naruto uses lately. Not much more about him is known at the moment.