Douwd
The Douwd were a species able to manipulate their appearance, self-described as "immortal beings of disguises and false surroundings". They had the ability to destroy on an epic scale. They also had the ability to create illusions sufficient to pass as real to both sensors, transporters the physical senses and empathic abilities. They could not bring people back to life, only make such illusory recreations of them. They had the ability to either exist and travel in non-corporeal form, or to transport themselves non-corporeally through space. The Douwd appeared to be nearly omnipotent godlike beings, but not omniscient.

One individual from the Douwd race was revealed to the Federation, a being who referred to itself as Kevin Uxbridge, while in Human form. He claimed to have lived in the Milky Way Galaxy for "many thousands of years". While in Human form, he met a Human woman named Rishon. The two fell in love, and were married for fifty-three years. When an alien vessel attacked their home planet and killed Rishon, he committed genocide of the attacking vessel's entire species. ()

Appendices

Background information 
It is not explicitly established whether the Douwd are non-corporeal or whether the glowing humanoid shape that is briefly seen as Uxbridge disappears on two occasions is his true Douwd form, or is simply an effect of whatever process allowed him to disappear and move non-corporeally between locations. However, the  indicates that they are "energy beings"

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Species
Telepathic species
Non-corporeal species