Arceus is a legendary and rare pokemon. Arceus is thought to have created not only Sinnoh but the entire Pokemon Multiverse.
Arceus does not suffer fools gladly, and will attack in a violent rampage if betrayed or deceived. It also holds long grudges if angered. However Arceus also cares for the protection of the world and protected the entire planet from meteors which caused it to sustain heavy damage and losing its plates but a man called Damos returned them to Arceus. As gratitude for saving its life, Arceus granted him the Jewel of Life which turned Michina Town from a wasteland into a paridise.
Soon a man called Marcus betryaed Arceus by stealing the Jewel of Life which caused Arceus to bare a grudge against Michina Town for a very long time.