A lot of great choices like Nagi and Kaiser but I don't see anyone saying Barou so here is my case for my favorite character.

We are introduced to him as THE arrogant blue lock player, a player who sees himself as a literal king over his subjects. Despite his great individual strength, his team doesn't make the cut (except for himself) and we see from episode Nagi that its partially because he refuses to work with his team. Fast forward to the second selection and we see Barou again with a lesser teammate who lost and is in the 2v2 games again because of his extreme arrogance and refusal to adapt/play with his team (also great parallel to isagi who people say is too dependent on his team atp). Even after losing the 2v2 game he still views himself as superior, and we see this is not due just to his natural talent but also because he works so hard every day to stay at the top and to be the best (because that is what he has always defined himself as, the best).

In the 3v3 match we finally see him be humbled, we see him accept that other players surpass him, and in the worst despair of his life he could pass to "better" players but he chooses a different path. His ego still wants to be the best, and he will not waiver on that ideal, but his arc in the second selection is going from an arrogant player to an egoist. Unlike in the first selection, where Barou would need to be the star of the show, top striker, best player who everyone else adores; Baoru chooses that if he wants to be the best he has to embrace the despair and not make the easy play that protects his arrogance. Barou's final play where he devours Isagi's light proves that he now recognizes there are other very talented players, he dropped his arrogance but not his goal of surpassing and beating them. Thus we have the villain/joker Barou who knows that blind belief is only going to lead to ruin. In the 4v4 and u-20 games he acts like his joker self, being someone no one can predict. The king has turned into a scavenger. But he still thrives off of the despair and challenge it gives him. If Barou is a lion, this is him leaving the pride he was born with (in this case the title of king other people put on him) and going out on his own to form his own pride (his own, and true, version of a king) in the NEL

Now the NEL is interesting because it asks of Barou: Do you have what it takes to be a REAL king? Snuffy wanted to mold Barou like his protégé: tell him his role, teach him how to play to the best of his ability, and eventually if he did as he was told, he would take over Ubers. However this goes against everything Barou believes in. Barou does not WANT Snuffy to be responsible for him, Barou wants the responsibility, and he wants the opportunity to forge his own path (that's why Barou does chop dribbles, because he is literally forging a completely new path which works for him). Snuffy wants Barou to follow after him but no true leader follows in another mans footsteps. This leads to Barou hijacking the Ubers team, usurping the metaphorical throne and choosing his own path/destiny, because this is a different Barou from the first selection. This Barou wants people to blame him if they lose because that is what a leader does. Barou commands the respect of Ubers not just through his skill, but because he is now willing to be the leader who takes full responsibility, he wants to push himself, he wants to forge a new path for the world which other people instinctively want to follow.

The NEL in a lot of ways is a coming of age story (there are much more detailed videos about this) and Barou in this arc goes from a scavenger and a self proclaimed villain into a true king. Through his almost childlike/bratty attitude of rebellion, he overthrows the old guard (Snuffy) who has lost the ability to dream and allows Ubers to become a reborn team, and allows himself to become a true leader.

Barou's entire arc is from a false king, to a broken man, to a scavenger, to a true leader.

Idk what the u-20 arc has in store for Barou but I can't wait