The protagonist in this particular book by J.K. Rowling is Harry Potter. In this book he is joined by his friends Ron and Hermione on an adventure to save the wizarding world. In this book he overcomes many obstacles like defeating Voldemort proving that this character has a lot of bravery and skills. Even as he does this he remains very modest. He has undoubtedly saved Hogwarts if not the world but after it is all done he won't even admitt it. In this book he is also a very big hero because he wants the sorceror's stone but not to use it for its power. He wants only to keep it away from Voldemort so he can't come back to power. Another big thing about Harry Potter is that he is very loyal. This is shown by the fact that in the beginning of the book Harry knew no one but by the end had a very close circle of loyal friends. He also shows his loyalty by being faithful to his house at Hogwarts called Gryffindor. Another example of Harry being modest is him not basking in glory when he helps out the quidditch team even when he breaks many records at a young age. His loyalty is also shown by his willingness to put himself in harms way to protect a friend.
In conclusion the protagonist, Harry Potter, is very loyal, modest, and above all he values the lives of others in front of his own.