Actually, who created Rasengan is still up for grabs at the moment. I personally believe the 4th created it...just from my interpretation of a translation so there always is a chance the meaning was lost in translation. Does anyone remember how long it has been since Jiraiya left Konoha? I think it said somewhere but I don't remember. But I thought it was a little after the 4th died, since he knew what Naruto was holding in his body. I believe that Naruto is somewhat of a genius at more difficult ninjutsu...you don't always have to know the basics to learn harder things. It's sort of like autistic people who can do square roots in split seconds and yet can't multiply for their life. Another thing is Naruto learned Rasengan, but he didn't perfect it. There is a difference. Naruto still "cheats" in a sense when doing Rasengan, and it is nowhere on the level of Jiraiya's (not to put down the accomplishment of course. The fact that he was able to learn it at all says a lot about his talent and hard work).