Voice actors behind Roronoa Zoro are:
There are multiple versions of One Piece dubbed in English, and they used different actors. In the original Japanese version Roronoa Zoro's voice is done by Kazuya Nakai. The English version made by 4Kids Entertainment used Marc Diraison for adult Zoro voice and Andrew Rannells for young Zoro voice. The other English dubbed version is made by Funimation and the voice actors are Christopher Sabat for adult Zoro and Cynthia Cranz for young Zoro.
Live impersonation of Roronoa Zoro by Kazuya Nakai
Live impersonation of Roronoa Zoro by Christopher Sabat