The Shimmer

The Entity from the Southern Reach Trilogy and the 2018 film "Annihilation" is an amorphous being of unknown origin that crash landed on Earth and began to terraform the surrounding area and create what is known as Area X.

Landing in the middle of a lighthous off the coast of Florida, the Entity began to create a constantly expanding bubble-like barrier where everything that entered it began to (in a metaphorical sense) become refracted like light in bizarre ways such as the DNA of various organisms inside begin to alter. The barrier was given the name "The Shimmer" and the area inside was titled "Area X" and as it began to expand overtime, civilization began to deteriorate with vegetation and fungi growing at an exponential rate and turning what use to be a small quite town into an alien forrest of monsterous creatures of what use to be normal animals. As Area X was studied by a secret organization known as the Southern Reach, various expeditions were sent into Area X with all of them never returning exept emotionally empty duplicates of the expedition members who mysteriously return to the homes of who they appear to be without any trace of how they got their.

It is unknown what intentions the Entity has for creating Area X or the empty duplicates (if any at all). Based on the Entity's encounter with the Biologist of the twelfed expedition were the Entity begins to change using the DNA from her blood to transform into a humanoid appearance and begins to mimic her, as if it was studying her movements and actions. Over time the Entity began to take on the appearance of the Biologist as their encounter progressed (which inheritly explained the doplegangers). In the 2018 film "Annihilation" which was based off of the first book in the Southern Reach Trilogy, the Entity was killed by the Biologist by tricking it into killing itself with a flash bomb which led to destruction of the Shimmer and Area X reverting back to its previous state. However it is implied that the Entity survived through the doppelgängers it has created.