Roronoa Zoro, the swordsman and sub-captain of the Straw Hat Pirates, is a character obsessed with becoming stronger, which makes sense considering he has big dreams of one day becoming the greatest swordsman on the planet. However, while there have been many story arcs throughout One Piece that have allowed Zoro to progress in terms of his power and strength thanks to a bit of training or by acquiring a new sword, and he's also experienced quite a bit of growth emotionally too.