The creature in Norse mythology that is a serpent encircling the Earth is Jörmungandr, also known as the World Serpent. Jörmungandr is one of the children of Loki and is said to be so large that it can wrap around Midgard (Earth) and bite its own tail. This creature plays a significant role in Norse cosmology, particularly in the events leading up to Ragnarök, where it confronts Thor in a high-stakes battle. Its imagery symbolizes the cyclical nature of life, death, and the struggle between order and chaos.