Giratina is a Legendary Pokémon of the Ghost/Dragon type. It is said to have been sealed away by the creator god, Arceus, for being too violent. Giratina was imprisoned inside an alternate dimension known as the Distortion World. 
Giratina is highly aggressive and protective of its home, but has a gentler disposition around humans. It used to bear a grudge against its creator Arceus, but has now reformed and protects the universe against threats such as Team Galactic and their leader Cyrus.