Well if you think about it, Naruto does resemble the 4th a lot. Their hairstyle especially. Also, Jiraiya mentions their hair and stubborness is too same. Jiraiya, having to teach both Naruto and the 4th, would know that best. I think the 4th is a relative of Naruto because there is no way Naruto is a reincarnation of the 4th. I think the 4th is still alive and the leader of Akatsuki but then Naruto is merely like a son or brother, relative, etc. Or maybe he is a homunculus created by the 4th >_>
If anything, it should be a relative of the 4th. It's just stupid if Naruto IS the reincarnation of the 4th because that garantees his success as a Hokage, which makes the story look stupid because its too obvious.
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The part where naruto is being held as a baby could've been the 4th as well. No one can prove if the 4th died RIGHT after using Shiki Fuujin technique. Apparantly, having to perfect Shiki Fuujin, the 4th probably knew a way to escape death from the Death God. But that is a possibility that the 3rd raised Naruto up as a child. High possibility in fact.