Monk

''"We will be invited. We will take this world, we will rule it's people, but only when we're asked." - Leader Monk''

The Monks are a highly advanced and intelligent race of invaders with the capability of taking over entire planets in days.

Biology
Even though the Monks resemble walking corpses dressed in red or orange robes, it is hinted that this is not there true form but is the form they chose to appear as to appeal to humans when they tried to take over Earth. But (while it is unknown by how different the Monks are from other creatures) they see humans as corpses, hence their appearance.

Technology
One thing that often differentiates the Monks from other planet invaders is their technology and how they use it. Their ships resemble five-thousand-year-old pyramids equipped with a tractor beam at it's peak to protect itself from airborne weaponry such as missiles and attack ships. Even though the Monks invade planets like most aliens in sci-fi, they instead practice their invasion tactics before even attempting to set foot on the planet they wish to rule. They are capable of creating holographic simulations (reminiscent of the holodeck from Star Trek) of various different areas and time periods of the targeted planet and practice how they should begin their invasion. The Monks possess giant transmitter statutes that specifically target the memory and perception of the brains of the species they control after their invasion. These statues transmit a signal that makes the controlled species believe the "True History" that the Monks have always been with them and that they have been guiding their civilization towards greatness. Inside the Monks' pyramid ship, a single immobile monk with a reflective a circular head is used to transmit the "True History" to the statues. Even before their invasion, the Monks have the ability to spy on their targeted planet by hacking into security cameras and even controls manners of basic and primitive technology from their ship.