I can think about a few but the one that always will come to my mind first is Itachi Uchiha. I will always say that his story (also Sasuke's) is far more interesting than Naruto's. It has a dark plot full with drama, tragedy, love, regret and many other things that make you feel a mix of emotions.
Hehe, when I read several days ago I thought of talking about Itachi, he is definitely a character that could have easily been the protagonist of Naruto, even Kakashi also has an excellent story and weight, but yes, definitely Itachi would have been tremendous protagonist.
Omg yes! Kakashi is also a character with a really underrated story. Perhaps most of Naruto's characters are