of course he is his father although they never say it like that you could see the phisycal similarity. and if he is not the father who else obviously if naruto is going to become one of the most powerful ninja in the village his father cant be a dumb guy in the street who better to be his father than the fourth hokge. And everyone here says that why did the hokage sealed the fox in naruto, hasnt the evil fox power saved narutos but a lot of times, think about that.