Flugel

Flugel (フリューゲル) was the Great Sage, and a key figure in the sealing of the Witch of Envy 400 years ago. Though mentioned by name and title throughout the series, his identity as the Great Sage isn't revealed until Arc 6. Due to certain circumstances, his name has been erased from history, with his exploits instead having been credited to his disciple, Shaula.

Although Flugel's ultimate fate is unknown, Natsuki Subaru theorizes that he is the ruler of the Corridor of Memories.

Appearance
Not much is known about Flugel or what he looked like, despite his face being engraved on the Lugunican currency. It is presumed that his outfit resembled Shaula's in some way as she mentioned she dressed similarly to him.

Personality
Shaula mentioned that Flugel was a very smart, and intelligent person. He apparently stated how tiring it was to talk to Shaula multiple times, implying he was also exasperated of her antics. Both Petelgeuse and Volcanica spoke of him with respect and fondness respectively, indicating he was rather likeable.

History
Approximately 400 years before Subaru's arrival, Flugel and Daphne created the unique Demon Beast, Shaula for currently unknown reasons. He also met and formed a partnerships of sorts with Echidna before her death.

Flugel and his apprentice are said to have met the first generation's Sword Saint, Reid Astrea and the Divine Dragon, Volcanica in one of the Kingdom's five regional capitals–Flanders, located in southern part of the Kingdom, and blessed the grounds of Flanders so Earth Dragons would be born. After Satella, the Witch of Envy, suddenly went out of control and went on a rampage across the world, Flugel and Shaula met with Reid and Volcanica in the Kingdom's city of Flanders, forming an alliance with the heroes. The four heroes set their goals on defeating the rampaging Witch who mercilessly killed thousands and thousands of innocents and toppled one country after another. After realizing they were unable to kill her, Flugel and the rest managed to defeat her and seal her away in the Sand Dunes at the very East of Dragon Kingdom of Lugunica.

After they successfully managed to defeat the Witch of Envy, Flugel created the Pleiades Watchtower in the vicinity of the Evil Sealing Stone Shrine, and gave Shaula the task of watching over it, giving her the order to indiscriminately kill anyone who attempted to approach it. He also erased himself from history, giving Shaula all the credit for his role in the fight against the Witch for an unspecified reason. Some time after, the two of them planted a seed in the middle of the Lifau Highway; a seed that would later grow into a giant tree dubbed Flugel's Tree.

At some point, he entrusted Petelgeuse Romanée-Conti with a box containing the Witch Factor of Sloth. The tree would later be destroyed by Natsuki Subaru, in order to defeat the Hakugei. The Kingdom of Lugunica also engraved his face on one of their holy coins for unknown reasons.

Abilities
Great Power: As Flugel potentially had the power to kill Shaula, and played a role in the sealing of the Witch of Envy, Flugel is rumoured to have had a considerable amount of power. However, it is not known if Flugel actually fought the Witch herself.

Vast Intellect: Considering his title as the Sage and numerous legends surrounding him, Flugel was known for having been a very intelligent person, considered by many to rival the Divine Dragon himself, in terms of intellect. Throughout the centuries following Satella's defeat, numerous countries dispatched envoys to the Tower in order to make contact with the Sage and gain knowledge that was unable to be obtained in any other way.

Trivia

 * "Flügel" means "wing/wings" in German.
 * The author has stated that the box that he gave to Petelgeuse was made out of the Sage's bones, containing the Witch Factor of Sloth. Having said that, no concrete proof exists that the box was made specifically out of Flugel's bones as, just like how there were other Witches of Sin before the ones introduced in Arc 4, there likely were other Sages throughout history, meaning the box could have very well been made out of bones from a long-dead Sage predating Flugel's summoning to the new world.
 * Flugel seems to have vast knowledge of Earth's constellations. The first trial of the monolith he created required the person being tested to know the constellations Orion and Scorpius (as well as knowing that "Shaula" was the name of the brightest star in Scorpius). The name of the watchtower itself was "Pleiades", the name of a cluster of stars, and the floors were named after the stars within Pleiades (Merope, Maia, Electra, Taygeta, Alcyone, Celaeno, and Asterope respectively).
 * According to the author, the relationship between Flugel and Reid is similar to Suneo and Gian (characters from Doraemon series).
 * Shaula has stated that Subaru "smells" similar to Flugel.
 * The Kingdom of Lugunica engraved his face on their currency. It is possible the depiction that does not correspond with his true appearance, as it is unlikely any member of the Kingdom would ever have met him personally due to Flugel preferring to operate in secrecy.
 * The face on the coin is stated to be a handsome man with long hair and a sharp look.