Kashchey

Kashchey was a Phidian duke of the Ursus Empire and a member of the Ursine "Old Guard." He was closely associated with the ideology and legacy of the "Deathless Black Snake," a recurring force within Ursus history whose exact nature remains ambiguous. Rather than being defined solely as a vessel of a singular entity, Kashchey's actions, rhetoric, and political worldview strongly embodied the principles historically attributed to the Black Snake across multiple accounts.

(Source: Arknights Wiki)