Zero is the main antagonist who wishes to use Giratina's power to travel freely between dimensions. He owns a robotic maid named Infi who controls his mothership, Megarig. Zero's objective was to rule the Reverse World. He wanted to save it from all the pollution emptied into it by the real world. He also wanted to use the Reverse World's properties to get revenge on the real world.

He was once Newton Graceland's student in studying the Reverse World, but he became obsessed with Giratina's power and decided to capture it. Using a machine designed by Newton himself, Zero was able to capture and unleash Giratina's power. He used the machine to cause destruction in the real world by damaging the Reverse World.

Despite doing significant damage, he was finally defeated by the combined power of Shaymin, Giratina, and Ash when he was forced back into the real world, and he crashed his flying machine into a glacier. Upon impact, Dawn, her Pokémon, and many surrounding Mamoswine, froze Zero into the glacier itself, still inside of his machine. Officer Jenny arrests him in the end of the film, during the credits.

He makes another appearance in the credits of Arceus and the Jewel of Life where he is in prison. He was shown to be visited by Newton, who possessed a surviving copy of Infi which he was happy to see.

(from Bulbapedia)