It's best to be yourself, I mean sure you can play one of the historical characters if you want, but the story isn't going to reflect that in the game.
I think it's based off an individual basis the game was kind of like a clean slate meant for you to feel individualized in the story of the game, kind of like how games like Skyrim work, you could be any race any gender, and you exist in this world, however because the game is linear when it comes to the main story, you could choose to do a playthrough where you're not the dragonborn so long as you have the right mods LOL.