Liu Zheng
Liú Zhèng (劉正 Ryūshō) is a character mentioned in the original Hokuto no Ken one-shot. He was the 21st Hokuto Shin Ken successor who trained Kenshiro Kasumi's father, who in turned trained Kenshiro himself.
It should be noted that in Sōten no Ken, Ramon Kasumi (who later becomes Ryūken, Kenshiro's adoptive father) was actually trained by his father Tesshin Kasumi, who is the 61st successor of Hokuto Shinken, not the 21st.