Which giantess is the mother of Hel, Fenrir, and Jörmungandr?

The giantess who is the mother of Hel, Fenrir, and Jörmungandr is Angrboða.

Angrboða is a jötunn, or giantess, in Norse mythology and the mate of Loki. The Prose Edda identifies her as the mother of three extraordinary children: Fenrir, the monstrous wolf; Jörmungandr, the serpent that encircles Midgard; and Hel, ruler of the realm of the dead. Their parentage helps explain why the gods regard Loki’s family as a growing cosmic threat.

According to Snorri Sturluson’s Gylfaginning, Odin has the three children brought before him after learning of their dangerous destinies. Jörmungandr is thrown into the ocean surrounding the world, Hel is assigned authority over the dead in Niflheim, and Fenrir is eventually bound by the gods. All three later play major roles in Ragnarök.

Angrboða’s name is commonly interpreted as “she who brings sorrow” or “harm-bidder.” She is sometimes confused with Jörð, a personification of the earth and Thor’s mother, but Jörð is not the mother of Loki’s three monstrous children. Angrboða is also associated by some scholars with the giantess of Ironwood, though that identification is interpretive rather than explicit.