Erlkonig (アールキング, Ārukingu)? is a recurring demon in the series.
The Erlkonig (Alder King), or Erlking, is a character depicted in a number of German poems and ballads as a malevolent creature who haunts forests and carries off travelers to their deaths. The name is an 18th-century mistranslation of the original Danish word elverkonge, "elf-king."
Erlkonig controls a Domain found in the Yoroi Shrine. The Yata no Kagami is obtained after his defeat.
Shin Megami Tensei IV Apocalypse
Erlkonig can teach Nanashi the Maziodyne, Stun Needles and Myriad Arrows skills through his Demon Whisper. He benefits from learning Gun, Electricity and Darkness skills.
Devil Summoner: Soul Hackers
"An evil wood spirit appearing in Germany's Scharzwald. He charms people and leads them to their deaths. His name means "Alder King," and true to his name, he is the ruler of the alders of the forest. It is said that the Erlkonig is the strongest of the alder trees."