In Slavic mythology, the creature known to guard the underworld is the Vodyanoy, a water spirit associated with rivers and lakes. Often depicted as a humanoid figure with features of fish, the Vodyanoy is both a protector and a trickster, capable of dragging unsuspecting souls to watery graves. This figure symbolizes the mysteries of life and death, embodying the natural forces that govern mortality and the eerie beauty of the aquatic realms.