The name of the giant serpent in Norse mythology that encircles the earth is Jörmungandr, also known as the Midgard Serpent. According to legend, Jörmungandr was thrown into the sea by Odin and grew so large that it surrounds the world, biting its own tail. This serpent represents the connection between the realms of gods, humans, and giants, signifying balance and cosmic unity. Its role in Ragnarok, the apocalyptic battle, underscores the themes of fate, destruction, and rebirth in Norse cosmology.