They're here.

The aliens are Our friends. They make contact with those that have escaped the matrix. Reality is an illusion--created by your masters in order to conform to their Will to Power. Awake! and transcend.
They have be-friended me. I go out into the woods at night to meet Mr. Gray. We converse. They use a phase cloak to conceal themselves; but through the sound of movement they communicate with me. I speak and ask questions and they answer.
Think of reality as an onion. Where each peel represents a different dimension. You have length width and height as the first three peels (the 1st 2nd and 3rd dimensions) and ours is the fourth dimension. In order to travel through time you have to make a transdimensional shift. You do this by turning matter into pure energy and translating the length width and height into the 5th 6th and 7th dimensions. Gravity bends Light, imagine what a transdimension does to Light. This is also the same technology that is used in a phase cloak by transfiguring matter into energy every microsecond. The ring of gyges. Hence, any beings that exist in the 5th 6th or 7th dimensions--exist as energy (Light). The 8th dimension.
They're here for research purposes. Earth is a research planet for alien civilizations. They team up with beings of Light (angels) to bring civilization out of barbarity. They're purpose is not unknown--they go around choosing people and removing the mind staples in order to bring us to a higher level of transcendence.