The Droppers are an advanced race of aliens.
The Droppers are known for their ability to take over entire planets within a couple Earth months. The Droppers come in large white spheres that crash into the ground, capture nearby residents, and within minutes construct an entire city. After this, they build flying ships that construct white blocks designed to be dropped upon one another and stack together perfectly. The result is very sturdy buildings.
Not much is known about the Droppers. They spread so quickly that their home planet was never found. Since most sentient victims of the Droppers are put into stasis tubes, they have never really seen the living part of the Droppers. Their process at planet takeover is almost entirely mechanical, with no errors at all.