Back in his homeland, the young Roronoa Zolo had been somewhat of a troublemaker until he decided to cause trouble in a kendo school. He dared to challenge someone from the school to a kendo duel. If he won, he'd steal their school sign. If he lost, he'd become a student. However, he didn't count on two things. First, his challenger was a girl named
Kuina. Second, despite choosing to fight with two swords, he lost to her.
It was the beginning of an intense rivalry. Zolo began to train like mad, and every day he'd try once again to beat Kuina. 2000 times he tried, and 2000 times he failed. Finally, for their 2001st (and last duel), the two agreed to fight a duel with real swords. Though Kuina once again bested Zolo, Kuina's heart was just not into it anymore. She was emerging into adolescence, and the traditions of their village prevented her from taking up her father's leadership of the dojo (in fact, it had been Zolo's constant challenges that had kept her going as far as she had). Zolo refused to accept that, and the two agreed to continue training to become the best swordmaster in the world.
However, Kuina's dream was cut tragically short not long after, even as Zolo had begun to work on a means of wielding a third sword in his mouth. After Kuina's could no longer fight (she died in the manga and Japanese version of the anime, and was severely injured in the 4Kids American dubbed version of the anime), he asked for (and received) Kuina's sword as a gesture to continue the dream they both had, so she could become stronger through him. He keeps her memory alive each time he wields this third sword between his teeth. After many more years of training, Zolo finally set out to prove his worth against the world.
Zolo soon amassed a fearsome reputation. Originally part of a small gang of pirate hunters, he became separated. By a strange turn of events, he happened to tick off the spoiled son of a rogue naval captain named "AxeHand" Morgan, when the man sicked his rabid wolf in a bar for kicks and Zolo attacked it to save a little girl. Morgan's son threatened to destroy the village if Zolo wouldn't be his prisoner for a month.
But it turned out Morgan's son was as dishonorable as his old man and intended to have Zolo executed. It is at this point, three days before Zolo's time was up, that Luffy showed up, looking for the famous pirate hunter. In exchange for his swords and his freedom, Zolo agreed to be part of Luffy's crew. The two of them proceeded to clean house, freeing the people from Morgan's reign of terror (much to his Naval officers' enjoyment), and the rest is history.
Zolo will not let anything interfere with his quest to become the best swordsman in the world. Luffy doesn't mind it and in fact encourages it. After all, it's only fitting that the Pirate King have the best swordsman by his side. But in that, Zolo can do some odd things. He tends to ignore pain and wounds when he's engaged in a fight (he's in his fighting mode when his black bandanna tops his head). He will never turn down a challenge by another swordsman, and he'll push himself to the limit.
When the bandanna is on his arm and he's resting, though, he can be remarkably lazy. He's been known to take naps at all sorts of strange times and places.
Eventually in the series, Zolo learns a technique called the Lion's Requiem, which can cut through anything that breaths. And according to the anime, almost everything, even metal, breaths in a way, allowing him to cut through almost anything. It is his most well known technique.
Zolor was born on Sasori Island.