Koschei

Here's my vision of Koschei (or Kaschei, Kashsei, Koshchai...), nicknamed the "Immortal" or the "Deathless", a recurring antagonist in Russian folklore. He's some sort of warlock King, who separated his death from himself through dark magic, and hid it in mysterious protected places varying from one tale to another. He often abducts and sequesters women, may they be princesses or just the male hero's love interest/wife. Sometimes the imprisoned woman is Koschei's own daughter, but she tricks him into revealing his death's hiding place, so she can help the male hero.

Koschei has been featured in many Russian ballets, operas and movies, including Stravinksy's "Firebird". He also can be seen as the origin of liches in Heroic Fantasy, and even J. K. Rowling's Lord Voldemort, to some extent.