Jörmungandr in the context of "Gosforth Cross"

Loki is a god in Norse mythology. He is the son of Fárbauti (a jötunn) and Laufey (a goddess), and the brother of Helblindi and Býleistr. Loki is married to the goddess Sigyn and they have two sons, Narfi or Nari and Váli. By the jötunn Angrboða, Loki is the father of Hel, the wolf Fenrir and the world serpent Jörmungandr. In the form of a mare, Loki was impregnated by the stallion Svaðilfari and gave birth to the eight-legged horse Sleipnir.

Like other gods, Loki is a shape shifter and in separate sources appears in the form of a salmon, a mare, a fly, and possibly an elderly woman named Þökk (Old Norse 'thanks'). While sometimes friendly with the gods, Loki engineers the death of the beloved god Baldr. For this, Odin's specially engendered son Váli binds Loki with the entrails of one of his sons, where he writhes in pain. In the Prose Edda, this son, Nari or Narfi, is killed by another of Loki's sons, who is also called Váli. The goddess Skaði is responsible for placing a serpent above him while he is bound. The serpent drips venom from above him that Sigyn collects into a bowl; however, she must empty the bowl when it is full and the venom that drips in the meantime causes Loki to writhe in pain, thereby causing earthquakes.

A sea serpent is a type of sea monster described in various mythologies and religious texts, most notably Mesopotamian (Tiamat), Ugaritic (Yam, Tannin), Judaic (Leviathan, Rahab), ancient Greek (Cetus, Echidna, Hydra, Scylla), Vedic (Vritra,Surasa) and Norse (Jörmungandr).

Fenrir (Old Norse 'fen-dweller') or Fenrisúlfr (Old Norse "Fenrir's wolf", often translated "Fenris-wolf"), also referred to as Hróðvitnir (Old Norse "fame-wolf") and Vánagandr (Old Norse 'monster of the [River] Ván'), is a monstrous wolf in Norse mythology. In Old Norse texts, Fenrir plays a key role during the events of Ragnarök, where he is foretold to assist in setting the world aflame, resulting in the collapse of humanity and society, and killing the god Odin.

Fenrir, along with Hel and Jörmungandr, is a child of Loki and female jötunn Angrboða. He is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda and Heimskringla, composed in the 13th century. In both the Poetic Edda and Prose Edda, Fenrir is the father of the wolves Sköll and Hati Hróðvitnisson, is a son of Loki and is foretold to kill the god Odin during the events of Ragnarök, but will in turn be killed by Odin's son Víðarr.

Angrboða (Old Norse: [ˈɑŋɡz̠ˌboðɑ]; also Angrboda) is a jötunn in Norse mythology. She is the mate of Loki and the mother of monsters. She is only mentioned once in the Poetic Edda (Völuspá hin skamma) as the mother of Fenrir by Loki. The Prose Edda (Gylfaginning) describes her as "a giantess in Jötunheimar" and as the mother of three monsters: the wolf Fenrir, the Midgard serpent Jörmungandr, and the ruler of the dead Hel.

Atter is an older Germanic term for "poisonous bodily fluid", especially venom of a venomous animal, such as a snake, dragon or other reptile, but also other vile corrupt or morbid substance from the body, such as pus from a sore or wound, as well as bitter substance, such as bile. Figuratively, it can also mean moral corruption or corruptness; noxious or corrupt influence, poison to the soul, evil, anger, envy, hatred; as well as destruction and death.

Today, atter is commonly associated with the Norse mythology, where it plays an important role in various contexts – see subsequent section: § In Norse mythology. In Eddic poetry, both the sea serpent Jörmungandr, and the dwarf Fáfnir in dragon-hamr, are described as having attery breath. A similar creature from later Orcadian folklore is the attery stoor worm which was killed by the hero Assipattle, falling into the sea and forming Iceland, Orkney, Shetland and the Faroe Islands. As in the English tale of the Linton worm, the stoor worm is killed by burning its insides with peat.