Koushirou Shimotsuki

, コウシロウ

Roronoa zoros teacher was named koushirou and he was kuinas father. he had his own dojo near where zoro grew up, and it was he who trained him. although he is typically seen in flashbacks, recently, in chapter 440, he made a brief appearance when another student asked if he was indeed roronoa zoros teacher. koushirou wished for zoro to continue pursuing his dream. it is implied that koushirou could cut steel as he followed the method of "swordsman who can cut nothing can also cut steel and anything else they wish." he tried to teach this skill to zoro when he was a child, but it wasn't until zoro turned 19 that he finally mastered it.

Spoilers:

It is revealed that, at least once in Shimotsuki Village (in a flashback), Koushirou helped the Revolutionaries by providing them food and supplies. He is seen talking with a man with a large face (possibly Emporio Ivankov) after dark, and Monkey D. Dragon even tells his army that they received food by the dojo, while preparing to set sail.