Now, Arceus.

Arceus is the God of Pokémon that has created everything and has been betrayed two times in Pokémon Legends: Arceus, and Pokémon: Arceus and the Jewel of Life, and he also has the power to speak telepathically, which he can make cries like a normal Pokémon would.

We already know what he looks like, because obviously, it's stated in his wiki if you want to know who Arceus is.