Who is/has been the most important “character” in the series?

I’m not entirely sure what I mean by this, but mostly…whose presence and actions have been most influential when it comes to lore/plotlines/relationships between the other characters?

There’s probably a case to be made for just about any of them, but I’ve gotta go with Jax or Kristen.

*(Not counting Lisa because that’s obvious. It’s her restaurant)