The Demogorgon

The Demogorgon, also known as the Monster, was a predatory humanoid creature that entered Hawkins, Indiana in November 1983. The creature originated from the parallel dimension known as the Upside Down. When Eleven, a psychic test subject from Hawkins National Laboratory, made interdimensional contact with it, a gate between dimensions opened at the lab. The creature then began hunting, killing and kidnapping various local townspeople.
The friends and family of Will Byers, one of the Demogorgon's victims, slowly began to uncover the truth about the creature, with the help of the escaped Eleven. The creature was finally defeated in a showdown at Hawkins Middle School, and Eleven used her telekinesis to incinerate the creature in a few seconds, turning it to ashes.