Fiction:Ultraterrestrials

The Inter-Dimensional Beings are a race of hyper-advanced beings native to another dimension or maybe even another plane of existence. Their technology is greater then most empires can even begin to fathom, they have the power to create entire dimensions and have existed for trillions of years, before the birth of even our universe. They are spread out across many dimensions, and create black-holes for use as energy sources.

Technology
Technologically, they are extremely advanced, capable to create so called pocket universe's, to trap an enemy in another universe without any means of escape, however, unlike many civilizations, they use their minds in their technology. For example they can use their mind to open up portals between different dimensions, and have integrated their weaponry with their psychic abilities, such as highly advanced psychic warfare, if any other empire found such a technology they could easily become one of the most advanced races in the universe.

Biological
Biologically, they are even stranger. In the billions of years of their evolution, they have evolved incredible psychic abilities, even looking into their eyes can cause madness, in even hyper intelligent creatures. This can be seen with their elongated cranium, and what is within, can cause paranormal activity in animals and in intelligent beings alike.

They are a Hive Mind, with all individual's separate, but at the same time connected. However they can function perfectly individually but they are always more powerful together.

In terms of intelligence, they are indescribable, they have long since lost the need to communicate telepathically. The individual Brain is much larger than a human and has 3 lobes. the third lobe is used for telepathic communication.

History
The history of the IDB's in clouded in mystery, but it is known that fairly recently, they visited Earth and were revered by early civilizations such as the Maya and the Aztec, who worshiped them as gods.

Thousands of years later they visited earth hundreds of times, and their Trans-dimensional vehicles became known as Flying Saucers and UFOs. When humans entered space, they found alien life but they never found the culprits against the UFO sightings.

Despite the fact that, they are so immensely powerful, they are relatively unknown by the empires of the first gigaquadrant, however they are numerous there. Undetectable by the other empires.