The Douwd were an extragalactic species made of pure energy, self-described as "immortal beings of disguises and false surroundings". They had the ability to create and destroy on an epic scale; they also maintained the ability to attack through psychic means. They could not bring people back to life, only make illusory recreations of them. The Douwd appeared to be powerful and godlike beings nearly omnipotent, but not omniscient.
The Douwd had a moral code which did not permit killing under any circumstances.
Only 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 lived a full Human life, meeting a woman named Rishon, falling in love, and being married to her for fifty-three years. (TNG: "The Survivors")