The High Priest (僧正 Sōjō) is a "bizarre magician", a magic god, who dwells in a territory beyond a certain layer of the world.
In the past, as a follower of the Japanese variety of Buddhism, the High Priest subjected himself to self-mummification, starving himself so his human form would transcend the six paths, becoming a Buddha in just one generation, in hopes of saving all people. However a faction opposed to him becoming a Buddha sabotaged his attempt and twisted as a result, he became a Magic God instead. At some point, he was somehow involved in the death of Aleister Crowley's daughter.
Powers and Stats
Name: Unknown. Commonly referred to as High Priest.
Origin: To Aru Majutsu No Index
Classification: Majin/Magic God
Powers and Abilities: Magic, Reality Warping, High Regeneration, Immortality type I and III (Possibly IV),Causality Manipulation, Changing the natural laws, Dirt Manipulation
Attack Potency: At least Hyperverse level (Superior to Aleister Crowley, who destroyed the Hidden World, a world that Othinus (A being who could freely manipulate, destroy, and create an infinite complex multiverse) couldn't even reach), possibly much higher
Speed: Immeasurable (Exists in the hidden world, in which the concepts of time and distance don´t apply)
Lifting Strength: Unknown. At least Superhuman, likely much higher
Striking Strength: Hyperverse level
Durability: Hyperverse level (survived the destruction of the hidden world)
Standard Equipment: Golden Sword
Intelligence: Very High
Weaknesses: He's very arrogant and looks down on everyone