Gin

Gin is fiercely loyal to Don Krieg, carrying out whatever orders he may be given from him no matter how inhumanly brutal or ruthless without protest or hesitation, thus earning himself the alias of "Gin the Demon Man."

This is partly due to a great fear of Krieg, which is evidenced when he obeys his orders to throw away his gas mask and breathe the deadly MH5 poison gas because he fears Krieg's wrath for disobeying more than death itself.

However, unlike Krieg, Gin has some sense of honor inside him, being unable to bring himself to kill Sanji, the very first person to ever show him kindness (by saving him from starvation).

(Source: One Piece Wikia)