Gin the “man demon” is the pirate and the combat commander of the Krieg Pirates. He is initially introduced as a mere combatant of Kreig before his actual ranks and abilities are made clear

Right now he was putting the gun on Zeff who was on the ground not moving. Gin looks up at Zeff real daughter your and then back at Luffy and Sanji..*

“Don’t move you all or I will end his life.”

He said.