Koshchei (Russian: Коще́й, romanized: Koshchey, IPA: [kɐˈɕːej]), also Kashchei (Russian: Каще́й, romanized: Kashchey, IPA: [kɐˈɕːej]) often given the epithet "the Immortal", or "the Deathless" (Russian: Бессме́ртный), is an archetypal male antagonist in Russian folklore.
The most common feature of tales involving Koschei is a spell which prevents him from being killed. He hides "his death" inside nested objects to protect it. For example, his death may be hidden in a needle that is hidden inside an egg, the egg is in a duck, the duck is in a hare, the hare is in a chest, the chest is buried or chained up on a far island. Usually he takes the role of a malevolent rival figure, who competes for (or entraps) a male hero's love interest.
The origin of the tales is unknown. The archetype may contain elements derived from the 12th-century pagan Cuman-Kipchak (Polovtsian) leader Khan Konchak, who is recorded in The Tale of Igor's Campaign; over time a balanced view of the non-Christian Cuman Khan may have been distorted or caricatured by Christian Slavic writers.