In Norse mythology’s Ragnarok, Thor dies after killing the Midgard Serpent.
The Midgard Serpent, or Jörmungandr, is the enormous snake that encircles the human world. It is a child of Loki and Angrboða and one of the great enemies destined to meet Thor at Ragnarok.
Thor kills the serpent with his hammer, Mjölnir, but its venom reaches him. The surviving myth says Thor walks nine steps before collapsing and dying. This closely matched exchange is one of Ragnarok’s clearest examples of victory carrying an immediate fatal cost.
Thor and Jörmungandr also meet in earlier episodes, including a fishing tale in which Thor pulls the serpent from the sea but does not kill it. That earlier encounter foreshadows their final confrontation, while the “nine steps” detail belongs to Thor’s death at Ragnarok.