Zoro's past reaches back to when he simply into the a small backwater school of kenjutsu. His challenge: if he would win he could take the school's sign, if he loses he would join the school to learn under the master. The challenger? The daughter of the master, Kuina. When Zoro picked up two swords, the other schools attendants were amazed. This awe was soon lost, when he was defeated by Kuina with a single parry and swing. Zoro showed an amazing amount of skill, yet this was the first time he had every picked up a sword. The master was quite pleased and began to teach him the studies of kenjutsu. During this time, Zoro trained not only from the school's own training but his own personal training of Two Sword Style. He trained twice as hard as any of the other students, yet every day he challenged Kuina and lost. Years later, when Zoro lost his 2000th match, he challenged Kuina to a different form of fighting. This time with real swords. Kuina defeated Zoro with almost no problem, disarming both of his swords. Zoro started to cry and scream about how he will one day be able to beat her. Kuina than commented subject on how she will never have the chance to become a great Swordsmen. She told him that women could not become great swordsmen. He retorted, screaming and covered in tears that they will both will train and become the greatest swordsmen of all time. She agreed.
Of course, not all stories have a happy ending. Kuina was killed by a falling accident off the rooftop of the warehouse. Zoro was angry and remorseful at the lose. Determined to become the best swordsmen for the both of them, he taught himself a strange form of three sword style of Kenjutsu. One that requires the use of his mouth to hold a sword. After years of training he left his masters side with two things to remember them by, the promise made to Kuina and her sword.
After this time, Zoro builds up a reputation to being a ruthless pirate hunter. He went a series of bounty hunts but eventually was split up from his two partners. Some time later he meet Luffy and was tricked into becoming a pirate.