Mercury

"I am the duality of the universe. I am both everything and nothing. I am man and woman. I am death and life. I am what has been and what is to come. I am destruction and the rebirth of everything afterward. I am more than what you will ever experience or comprehend. I can offer you so much more."

Mercury has a god complex and an ego that rivals planets' sizes. They show no remorse or care in what happens, the only thing that matters is that they are on top (where they believe they belong). Coming to Earth didn't help that as they were revered as a god by humans, who they saw as weak and pathetic but the control over an entire planet/species was too hard to resist. Their current hold on humans is less than it used to be, but they still have loyal followers in the cult they've developed over the years. They promise immortality and riches (which they figured out was a strong desire in humans) to those who follow. They will kill and attack without warning as well, and their fluid body allows them to navigate doing so.