<p>I'm going to go ahead and say something extremely unexpected.
</p><p>Naruto.
</p><p>[Intelligence is a] very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings—"catching on," "making sense" of things, or "figuring out" what to do.[ Gottfredson, Linda S. (1997). "Mainstream Science on Intelligence]
</p><p>Well, Naruto does that. A lot, and very well. He reasons, plans, solves problems. He's not very good at abstract thinking because he never got taught that very well. However, he easily comprehends complex ideas. He lacks the knowledge to actually realize he does understand it. But i'll just remind people when he spread his chakra to the Alliance to facilitate their transport. he came up with the idea of spreading chakra, making contact to his father and so allowing him to transport everyone out. Since he was taught pretty poorly early in his life he was never taught properly about chakra, but nevertheless came up with the idea and executing it without fully understanding the mechanics behind them. He knew these mechanics had to exist, he simply lacked the knowledge to know what they were.
</p><p>Similarly, he learned rasengan by dealing with his own problems and using his own strengths, had the emotional intelligence to stand up to Pain, and found creative ways to deal with Kaguya.
</p><p>In the end, he's seen as stupid because he simply lacked years worth of education, because he lacked parents, their guidance and a school system fit for him. But he's a lot smarter than people give him credit for, and it's definitely acknowledged by even the ones considered the smartest like Tobirama and Minato.
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