In Norse mythology’s Ragnarok, Heimdall fights Loki, the father of Jörmungandr, and the two kill each other. Loki is the trickster figure whose children include Fenrir, Jörmungandr, and Hel with the giantess Angrboða.
Heimdall’s final combat is especially notable because it mirrors his role as the gods’ watchman. He sounds the Gjallarhorn before the battle, then meets Loki in the last conflict. The surviving mythic accounts do not present this duel as a victory for either side: both die.
This should not be confused with Thor’s battle against Jörmungandr. Thor kills the Midgard Serpent but then dies from its venom. Heimdall’s opponent is Loki, Jörmungandr’s father, rather than the serpent itself.