Arceus created the Pokémon of Myth and the entire Pokémon universe. Known as the Original One, Arceus was worshiped in ancient times by the people of Hisui under the name Almighty Sinnoh. In its Normal-type form, Arceus is a white, equine Pokémon with an androgynous appearance. It resembles a qilin or centaur with a gray, vertically striated underside. The striated pattern also appears on the underside of its mane, tail, and face. Its four pointed feet are tipped with gold hooves. Its long mane juts away from its head, and its face is gray, with green eyes, red pupils, and a green circular pattern below its eyes. Arceus also has a streak of gold coloration on its head, which points upward. Its neck is fairly long, with two pairs of extrusions to the sides, and a flap-like feature on the neck's underside that is colored white like much of the body. Arceus also has a golden cross-like wheel attached to its body by its round abdomen. The wheel also has four green jewels attached to it. The pattern of striated gray of Arceus's underbelly continues past its waist. Its limbs have gray undersides and extrusions at the tops of the legs. Arceus's tail is similar to its mane in terms of shape and coloration. Despite its quadruped appearance, Arceus is capable of flight. In its Normal-type form, Arceus is a white, equine Pokémon with an androgynous appearance. It resembles a qilin or centaur with a gray, vertically striated underside. The striated pattern also appears on the underside of its mane, tail, and face. Its four pointed feet are tipped with gold hooves. Its long mane juts away from its head, and its face is gray, with green eyes, red pupils, and a green circular pattern below its eyes. Arceus also has a streak of gold coloration on its head, which points upward. Its neck is fairly long, with two pairs of extrusions to the sides, and a flap-like feature on the neck's underside that is colored white like much of the body. Arceus also has a golden cross-like wheel attached to its body by its round abdomen. The wheel also has four green jewels attached to it. The pattern of striated gray of Arceus's underbelly continues past its waist. Its limbs have gray undersides and extrusions at the tops of the legs. Arceus's tail is similar to its mane in terms of shape and coloration. Despite its quadruped appearance, Arceus is capable of flight. Arceus does not suffer fools gladly and will attack in a violent rampage if betrayed or deceived. It also holds long grudges if betrayed by those it considered friends. In Hoopa and the Clash of Ages, it was shown to be able to stop the destruction caused by a space-time void. As shown in the Pokémon Journeys: The Series episode Showdown at the Gates of Warp!, Arceus has the power to not only calm Dialga and Palkia, but also destroy the Red Chain controlling them. It can release countless shots of light that disintegrate the landscape around it. Arceus can change its type at will to adapt to a situation through the use of its Plates or type-specific Z-Crystals. Arceus also has the power to split in two, creating a piece of itself to exist outside of its realm, which is implied to be its physical form—only a piece of its whole being—while its true form is unknown and incomprehensible. Arceus was known to care for and safeguard the planet in ancient times, protecting the world from cataclysms such as meteors, and it would show gratitude and compassion to those who treated it with kindness. In modern times, Arceus continues to watch over the world and wishes for people and Pokémon to work together in the face of adversity. Even when it is needed, it only gives hints on how to solve problems instead of directly interfering. Arceus can also give its blessing to other Pokémon through bolts of light, making them bigger and more powerful, as seen with the ancient hero's 10 Pokémon companions. Like the Pokémon it created, Arceus also resides in another dimension, a realm beyond time and space itself. There, it appears in a form made of golden light, shaped like the silhouette of its normal appearance. This could possibly be its true form. It was also shown to be capable of human speech, stating that "Arceus" is simply the name humans call it. The ancient Sinnoh people worshiped it, referring to it as "almighty Sinnoh," "great Sinnoh," and "might of Sinnoh," with the term "Sinnoh" later on becoming the name of the region. The Diamond Clan and Pearl Clan also worshipped it, though they mistook Dialga and Palkia respectively for Arceus.

The Temple of Sinnoh is a ancient monument atop Mount Coronet in the Sinnoh region, originally built in honor of the creator god Arceus, as revealed in Pokémon Legends: Arceus. It served as a site for sacred rituals, but its advanced state in the present-day Sinnoh games is a partially destroyed remnant known as the Spear Pillar. This location is crucial as it contains the Hall of Origin, where Arceus resides, and was the site of events involving Dialga and Palkia, the gods of time and space.

a powerful, god-like being in the Pokémon universe, with a complex personality. It embodies a desire for order and evolution, actively shaping the development of Pokémon. It also acts as a guardian, ensuring balance and harmony in the Pokémon world, and intervening to prevent catastrophes. Arceus does not suffer fools gladly and will attack in a violent rampage if betrayed or deceived, it also holds long grudges if betrayed by those it considered friends and may act volatile in these situations.