Arceus

Arceus is known as the Pokémon of the Beginning, and was created by Sato and her siblings at the dawn of time. He is first introduced in Chapter 18 of Stun.

Arceus is responsible for creating Dialga, Palkia, and Giratina. And is considered the Pokémon God for those who are not familiar with Sato and her siblings, and is widely regarded as the strongest legendary Pokémon in existence; he claims to only answer to Sato.

Although Arceus's power is undeniable, he claimed that he had attempted to defeat Tenebrae multiple times by himself prior to the events of Stun, only to be terribly beaten each time.

It is revealed that some time between the the events of Stun II and Project Stun, Arceus was captured by humans and his DNA was used in the creation of Porygon-A, the most powerful weapon in the humans' armory.