Zoro had wanted to be swordsman ever since he was a child. He soon entered a dojo and was faced by the first person he had to overcome, the daughter of the dojo's master, a girl called Kuina who was extremely talented. She, however, was devastated by the thought that, being born a woman, she could never be as skilled as a man. Zoro made her promise that one day, one of the two would become the greatest swordsman/swordswoman of the world.

Unfortunatly, Kuina died soon after and so Zoro decided he would keep his promise by becoming the strongest swordsman himself, using his three-swords style (santoryuu). He encountered Luffy while being imprisoned by the Marines, was saved by him and decided to join his one-man crew. Now Zoro is determined to reach his goal, not only because of his promise to Kuina, but also because if Luffy is to become the Pirate King, he can't be anything less than the strongest swordsman.