Demaro Black also known as Fake Luffy, is a Pirate Captain that impersonated Luffy. He was the main villain of the Return to Saboady Archipelago Arc in One Piece.
Black is cruel and ruthless and will sacrifice his loyal crew to get what he wants. He only cared to use the name of Monkey D. Luffy to spread fear to the people on Saboady Archipelago. He only done this because he wanted a powerful crew to assist him in his adventures through the New World. Black is very arrogant and believes that he can do as he please since he fooled dozens of people into thinking he was the infamous Monkey D. Luffy. When he was confronted by the real Straw Hat Pirates, he did not believe they were the actual crew.
When he was confronted by the Sentomaru and the Marines, Black was afraid for his life and tried to escape by all means. It was revealed by Sentomaru that he was famous liar throughout the seas.
Black is a master lair. He was capable of fooling dozens of people that he was Monkey D. Luffy. He has superhuman strength and endurance. Despite his intimidating appearance and height, Black lacks any skills that would provide a challenge to powerful enemies like Monkey D. Luffy or Sentomaru and was defeated easily.