Jeon Jang-Il

He was a Sun-Woo Clan elder who became Shi-Woon Yi's teacher after Chun-Woo Han. Although his goal was originally to stop the fight between Shi-Woon and Ji-Gun Yoo by exhausting him through an extreme training regime, he later warmed up to Shi-Woon after he reminded him of the previous clan head with his determination.

(Source: The Breaker Wiki)