Hel, the Norse goddess of death, is a complex figure, Loki's daughter, who rules the gloomy underworld realm of Helheim, a place for those dying of old age or sickness, not just evil. She's often described as a grim, powerful deity, sometimes depicted as half-flesh, half-corpse (blue-black), embodying death's impartiality, ruling her icy realm from her hall Eljudnir, and guarding the dead with her guard dog, Garm.

Key Characteristics:
Parentage: Daughter of Loki and the giantess Angrboda, making her sister to Fenrir and Jormungandr.
Appearance: Often described as a fearsome figure, half beautiful and alive, half blue-black corpse, symbolizing the duality of life and death, notes World History Encyclopedia.
Realm: Governs Helheim, a cold, dark realm in Niflheim, distinct from the warrior's Valhalla, notes Norse Mythology for Smart People.
Role: Rules over the dead who don't die in battle (sickness, old age, accident), acting as a neutral, powerful force rather than purely evil, writes Valhalla Vikings.
Demeanor: Reserved, quiet, and powerful, a "queen of the dead,".

Symbols & Associations:
Symbols: Skulls, rakes, brooms, red roses, black/white/gray colors.
Animals: Garm (her wolf guard dog), black mare, hellhounds.
Runes: Ear, Raido, Hagalaz, Othala, Hagall.

In Summary: Hel is not the horned devil of popular culture but a formidable, complex goddess of the dead, representing the inevitable journey all mortals take, notes this article from Valhalla Vikings.