Ok lets see I know that Giratina, Dialga & Palkia are a trio I know that,but when you see the story of the creation and the pokedex and the anime, you see that they say something like "In a void of nothingness, a single egg comes into being, which then hatches into Arceus, the first Pokémon to be in existence. Arceus creates Dialga, Palkia, and possibly Giratina and gives Dialga and Palkia the abilities to control time and space. Giratina, for its violent behavior, is banished to another dimension. Then, during very early formation of the world, possibly sooner, Arceus creates Azelf, Uxie, and Mesprit to create willpower, knowledge, and emotion respectively, things that are in all modern humans and Pokémon". this What it says in bulbapedia, note that it says and possibly Giratina, so we don't really know don't, you see that in the games they never talk of the relation between Arceus and Giratina.