In the Poetic Edda, Prose Edda, and Heimskringla, Hel is referred to as a daughter of Loki, and to "go to Hel" is to die. In the Prose Edda book Gylfaginning, Hel is described as having been appointed by the god Odin as ruler of a realm of the same name, located in Niflheim. In the same source, her appearance is described as half blue and half flesh-coloured and further as having a gloomy, downcast appearance. The Prose Edda details that Hel rules over vast mansions with many servants in her underworld realm and plays a key role in the attempted resurrection of the god Baldr.
Scholarly theories have been proposed about Hel's potential connections to figures appearing in the 11th century Old English Gospel of Nicodemus and Old Norse Bartholomeus saga postola, that she may have been considered a goddess with potential Indo-European parallels in Bhavani, Kali, and Mahakali or that Hel may have become a being only as a late personification of the location of the same name.
Jacob Grimm theorized that Hel (whom he refers to here as Halja, the theorized Proto-Germanic form of the term) is essentially an "image of a greedy, unrestoring, female deity" and that "the higher we are allowed to penetrate into our antiquities, the less hellish and more godlike may Halja appear. Of this we have a particularly strong guarantee in her affinity to the Indian Bhavani, who travels about and bathes like Nerthus and Holda, but is likewise called Kali or Mahakali, the great black goddess. In the underworld she is supposed to sit in judgment on souls. This office, the similar name and the black hue [...] make her exceedingly like Halja. And Halja is one of the oldest and commonest conceptions of our heathenism."
Grimm theorizes that the Helhest, a three legged-horse that roams the countryside "as a harbinger of plague and pestilence" in Danish folklore, was originally the steed of the goddess Hel, and that on this steed Hel roamed the land "picking up the dead that were her due." In addition, Grimm says that a wagon was once ascribed to Hel, with which Hel made journeys. Grimm says that Hel is an example of a "half-goddess;" "one who cannot be shown to be either wife or daughter of a god, and who stands in a dependent relation to higher divinities" and that "half-goddesses" stand higher than "half-gods" in Germanic mythology.
Hilda Ellis Davidson (1948) states that Hel "as a goddess" in surviving sources seems to belong to a genre of literary personification, that the word hel is generally "used simply to signify death or the grave," and that the word often appears as the equivalent to the English 'death,' which Davidson states "naturally lends itself to personification by poets." Davidson explains that "whether this personification has originally been based on a belief in a goddess of death called Hel is another question," but that she does not believe that the surviving sources give any reason to believe so. Davidson adds that, on the other hand, various other examples of "certain supernatural women" connected with death are to be found in sources for Norse mythology, that they "seem to have been closely connected with the world of death, and were pictured as welcoming dead warriors," and that the depiction of Hel "as a goddess" in Gylfaginning "might well owe something to these."
In a later work (1998), Davidson states that the description of Hel found in chapter 33 of Gylfaginning "hardly suggests a goddess." Davidson adds that "yet this is not the impression given in the account of Hermod's ride to Hel later in Gylfaginning (49)" and points out that here Hel "[speaks] with authority as ruler of the underworld" and that from her realm "gifts are sent back to Frigg and Fulla by Balder's wife Nanna as from a friendly kingdom." Davidson posits that Snorri may have "earlier turned the goddess of death into an allegorical figure, just as he made Hel, the underworld of shades, a place 'where wicked men go,' like the Christian Hell (Gylfaginning 3)." Davidson continues that:
"On the other hand, a goddess of death who represents the horrors of slaughter and decay is something well known elsewhere; the figure of Kali in India is an outstanding example. Like Snorri's Hel, she is terrifying to in appearance, black or dark in colour, usually naked, adorned with severed heads or arms or the corpses of children, her lips smeared with blood. She haunts the battlefield or cremation ground and squats on corpses. Yet for all this she is 'the recipient of ardent devotion from countless devotees who approach her as their mother' [...].
Davidson further compares to early attestations of the Irish goddesses Badb (Davidson points to the description of Badb from The Destruction of Da Choca's Hostel where Badb is wearing a dusky mantle, has a large mouth, is dark in color, and has gray hair falling over her shoulders, or, alternatively, "as a red figure on the edge of the ford, washing the chariot of a king doomed to die") and The Morrgan. Davidson concludes that, in these examples, "here we have the fierce destructive side of death, with a strong emphasis on its physical horrors, so perhaps we should not assume that the gruesome figure of Hel is wholly Snorri's literary invention."
John Lindow states that most details about Hel, as a figure, are not found outside of Snorri's writing in Gylfaginning, and says that when older skaldic poetry "says that people are 'in' rather than 'with' Hel, we are clearly dealing with a place rather than a person, and this is assumed to be the older conception," that the noun and place Hel likely originally simply meant "grave," and that "the personification came later." He also draws a parallel between the personified Hel's banishment to the underworld and the binding of Fenrir as part of a recurring theme of the bound monster, where an enemy of the gods is bound but destined to break free at Ragnarok. Rudolf Simek theorizes that the figure of Hel is "probably a very late personification of the underworld Hel," and says that "the first scriptures using the goddess Hel are found at the end of the 10th and in the 11th centuries." Simek states that the allegorical description of Hel's house in Gylfaginning "clearly stands in the Christian tradition," and that "on the whole nothing speaks in favour of there being a belief in Hel in pre-Christian times." However, Simek also cites Hel as possibly appearing as one of three figures appearing together on Migration Period B-bracteates.