I find it interesting that the only main character besides sub-characters that bridges between a few main characters is Tyrion. He has been involved directly and indirectly with most the plot characters and has traveled more of the world. Tyrion has to be considered the main character even though Jon, Brienne, Bran, Davos, Arya and Dany seem to be the heroes of the book and show. Tyrion has ruled better than Dany and been in worse situations than Jon. He has murdered in anger like Arya. He has loyalty like Davos and Brienne. He is an underdog like Bran. Tyrion is the main character.