DISCLAIMER: This article does not feature any spoilers from the movie. All information is based on official pre-release material provided by Shueisha and Toei.
Douglas Bullet, known as the Demon Heir, is the main antagonist of One Piece: Stampede.
After serving as a child soldier in his homeland of Gultzberg, he joined the Roger Pirates and was later imprisoned in Impel Down for over 20 years. He escaped during the mass breakout caused by Monkey D. Luffy and Marshall D. Teach, and plotted to become Pirate King by luring the world’s most powerful people to the Pirates Expo and attempting to kill them.
Even for a former member of the Roger Pirates, Bullet is one of the world’s most powerful pirates. He has tremendous fighting skills and experience, having fought and survive in brutal wars since infancy, engaging in highly dangerous tasks and putting his life constantly at risk on the battlefield, but always surviving.
During his youth, almost no one could match Bullet in strength, and he did not meet defeat until he faced the future Pirate King Gol D. Roger. Buggy equated his strength at the time with Silvers Rayleigh’s, and speculated that Bullet had surpassed Rayleigh due to continuing to train while Roger’s first mate retired.
Bullet’s threat became so significant that a Buster Call was ordered solely to take him out, commanded by legendary Marines Sengoku and Monkey D. Garp; even still, Bullet put up an intense fight, and it took the assistance of pirates to finally overwhelm him.
Bullet ate the Gasha Gasha no Mi, a Paramecia-type Devil Fruit that allows him to disassemble inanimate objects and assemble them into anything he wants with his mind. With this power, he can form a large variety of mechanical creations, most notably creating exoskeletons to significantly augment his physical power.
Bullet has awakened his fruit, allowing him to disassemble objects from a greater range. With his awakening, he can essentially restructure the landscape of entire islands by assembling their features as he sees fit, and creating and inhabiting a colossus whose physical presence is unparalleled.
Bullet is one of the few people in the whole series capable of using all three types of Haki, and has shown using all three to great effect. So Douglas Bullet seems to be hyped as an absolute monster, even Yonko level by the way he’s described!