Magician

Magicians (魔術師, Majutsushi) are a special group of humans capable of using magic in High School DxD.

Summary
While all supernatural beings are shown to be capable of learning magic and spells, it is suggested that only humans can be called Magicians. It is said that the current magic system used by humans was developed by Merlin Ambrosius, the legendary wizard from Arthurian legend, who studied demonic power and their magic.

The magic system used by humans is categorize into two major types, Western magic and Eastern magic, Western magic is a system of spells and magical knowledge founded in Europe while Eastern magic is a system of sorcery that originate in Asia, magic used by humans originates from knowledge of Devil's demonic power and miracles of Gods of different religions.

Magicians were first introduced during Volume 4, when large groups of Magicians banded together with the Khaos Brigade in hopes of disrupting the peace process that the Three Factions were engaging in. They attacked the leaders, while kidnapping Gasper in order to use his Sacred Gear, Forbidden Balor View, as a weapon against them. Several Magicians were killed by Azazel, while Rias and Issei went to fight those who had Gasper imprisoned (all of whom were female). The Magicians were defeated by the power of Gasper that was unleashed by Issei's blood, and Issei's Dress Break spell.

In Volume 12, Azazel reveals that there is a Magician's Council of some kind, which appears to govern Magicians. Among its duties is releasing rankings for young Devils. In Volume 14, it is revealed that the current director for the Magician's Council is Mephisto Pheles. It is also revealed that the Magicians in Khaos Brigade are Magicians that were expelled by Mephisto and are known as Stray Magicians (はぐれ魔術師 Hagure Majutsu-shi).

In Volume 15, it is revealed that there are many other Magicians associations, "Nilrem" that is affiliated with Khaos Brigade, "Grauzauberer" that is under Mephisto Pheles, "Golden Dawn", "Rosenkreuzer" and "Hexennacht".

Powers and Abilities
Magicians are humans that have learned the spells of at least one of the various factions of supernatural beings. This gives them a wide range of abilities, limited only by their own knowledge and skill level. They include teleportation, seals, a wide range of offensive and defensive spells, and several others.

In Volume 14, Le Fay mentions that demonic power requires the power of using your imagination and the power to create, as well as having a good sense, while magic is just knowledge to control equations, i.e. using your head and making calculations. So while they may seem similar, they are very different from each other. Kuroka further added that magic is something where the user uses the knowledge and calculations to know "If I do this, this will happen".

There are three main reasons why a Magician would make a pact with a Devil:
 * 1) Protection: The first is to use them as their bodyguard. When the time comes, having a powerful Devil behind their back will allow them to talk with the opponents if they are caught up in a quarrel.
 * 2) Information: Secondly, Magicians make pacts because they want to attain the techniques and knowledge of Devils. To make it clearer, the technique standards of the Underworld. These things will play a large role when Magicians do their research. Also, by making a pact with a Devil, they will be allowed to get items/resources cheaper by having an equal exchange.
 * 3) Public Eminence: Lastly, they make a pact with a Devil for their own status. Making a pact with a powerful Devil will bring great fortune and success to them.

Known Magicians

 * Merlin Ambrosius (Founder)
 * Georg
 * Le Fay Pendragon
 * Faust (Historical)
 * MacGregor Mathers (Former)
 * Loup Garou
 * Walburga

Known Magic types

 * Norse Magic
 * Devil Magic
 * Angel Magic
 * Fallen Angel Magic
 * Black Magic
 * White Magic
 * Fairy Magic
 * Alchemy
 * Summoning Magic
 * Spirit Magic
 * Rune Symbols
 * Teleportation Magic

Trivia

 * Though antagonistic to the Three Factions, the "Hexennacht" are Stray Magicians in a separate division from the Khaos Brigrade's Magician Faction, "Nilrem".
 * The Norse are one of the central factions for magic.