Hela--or simply Hel, if one prefers--is the dark goddess of the Nordic underworld, specifically ruling two of the three categories of the dead: the common dead and the dishonored (or evil) dead. The virtuous and heroic dead are given the honored privilege of being escorted by both the Valkyries and Hela to a special section of Asgard called Valhalla (the Viking equivalent of Heaven), where half are ruled by Odin and the other half by Freya. Hela's jurisdiction extends over two underworld realms where shades of the Nordic dead congregate following their physical demise: Helheim or Hel (named after herself, much as was the case with her counterpart Hades in the Greek pantheon), also the location of her great palace, and where the common dead reside post-mortem in a bleak, mist-enshrouded environment; and Niflheim, a frozen realm of misery where the dishonored dead reside to their continual regret, which is the realm where the now nearly extinct race of primordial ice giants used to dwell.
Hela's control over the wills of most of the shades who exist in each of her two domains is complete, and legend has it that she put them to work in building a tremendous ship called Nafhlgar, said to be made of the fingernails of the dead. This ship, following its completion, is to be used to carry the enemies of the deities against the forces of the gods at Ragnarok, the fated cataclysmic "Twilight of the Gods."
As the above indicates, Hela is a highly bitter and sometimes outright wicked goddess, and she feels good reason to display these attributes. One of the three offspring of Loki (along with Jorumungand the Midgard Serpent and the Fenris Wolf) by the giantess Angrboda, Hela was said to be born with the left side of her body fully alive and healthy, while the right side of her body is dead and decayed. Not eager to have this being among them, but finding her useful in a specific and obvious capacity, All-Father Odin declared her ruler of the underworld realms of the common and dishonored dead, and gave her sufficient power to carry out this necessary function. This led to Hela carrying on a lonely existence where she has little regular contact with her fellow deities and mostly has only her ever-growing deceased subjects for company. Her seeming abandonment by her fellow deities was never appreciated by her, to say the least, and her nature was deeply affected by her role and the near-isolation from the living that it entails. She usually wears an enchanted cloak that conceals her freakish physical condition, but this hardly detracts from her anger and embarrassment over her partially corpse-like form that denies her the beauty enjoyed by all the other goddesses.
Two other divine beings are under Hela's thrall and assist in guarding certain parts of the underworld on her behest. One of them is the goddess Modgud, who guards the bridge leading into the Helway, the long winding passage leading directly into Helheim. The other is the huge and intelligent hellhound Garm, who allows anyone--living or otherwise--to enter the underworld, but will not allow anyone to leave there again without a very serious fight. In this role, he is quite similar to Cerberus, the huge and vicious canine guardian of the entrance into the Greek underworld--though Garm has only one head, and not three, as does Cerberus.
In her role as a death goddess, Hela is among the most powerful of all the deities, in her own way rivaling that of Odin. She seems to receive an uncertain but high degree of power from Death incarnate, one of the universe's most potent forces, to control the shades in her realm and over the death force itself. She can cause even a perfectly healthy living being to die simply by touching them. She is the only one of the deities other than Odin and Loki that I fear to invoke, and the only one to fill me with a sense of dread whenever I call upon her while in my magick circle. Though I hesitate to call upon her, there are reasons to do so at times, particularly the fact that she is very wise and able to grant brief communication with any shade that exists in any of the numerous afterlife realms, though she and other death deities are highly reluctant to do the latter, as they see a need to usually strictly enforce the already strong barriers between the material realm of the living and the astral realms of the deceased. Communicating with Hela can be fortuitous for the followers of the Norse path at times in order to acquire the wisdom she has to give, and she need not only be called upon for the casting of dark spellwork.
When I do call upon Hela, I often invoke her Germanic aspect of Holda, where she has the added attributes of being a goddess of wyrd or fate, and she can influence these aspects of mortals' lives. In this aspect of hers, she is often depicted as having the left side of her face black and the right side chalk white, which can be seen as an alternative way of visualizing the duality between life and death that she embodies. In her aspect of Holda, she has also been said to sometimes accompany Odin (in his Germanic guise of Wotan) on his jaunts across the skies of Midgard in the Wild Hunt, and at other times Holda is said to lead the much feared Wild Hunt on her own, accompanied by nine hellhounds that are alleged to be her daughters.
Hela, or her Germanic aspect of Holda, is seen as the Crone aspect of the Wiccan Triple Goddess for practitioners of Norse Wicca, and this exemplifies her status as a wise goddess whose nature precludes that you approach her with caution and respect in order to receive bits of that wisdom and insight into the great inevitability of death. As such, Hela can be seen to represent the more bittersweet aspects of death, even though this eventual and inevitable ascension of our consciousness to the Other Side is a highly necessary step in our spiritual growth and evolution, and hence should not be feared.