In the second book in the Legion of Space series, Jay Kalam, Hal Samdu and Giles Habibula fight The Cometeers, an alien race of energy beings controlling a "comet" which is really a giant force field containing a swarm of planets populated by their slaves. The slave races are of flesh and blood, but none are remotely similar to humans. The Cometeers cannot be destroyed by AKKA, as they are incorporeal from the Universe's point of view and exist for the most part in an alternate reality. The ruling Cometeers feed on their slaves and literally absorb their souls, leaving disgusting, dying hulks in their wake. It is said that they do so, as they were once fleshly entities themselves of various species. Hence, the ruling Cometeers keep other intelligent beings as slaves and "cattle." They fear AKKA, though, as it can erase all their possessions.
Jack Williamson (1908 - 2006)
John Stewart 'Jack' Williamson was born in Arizona in 1908 and raised in an isolated New Mexico farmstead. After the Second World War, he acquired degrees in English at the Eastern New Mexico University, joining the faculty there in 1960 and remaining affiliated with the school for the rest of his life. Williamson sold his first story at the age of 20 - the beginning of a long, productive and successful career, which started in the pulps, took in the Golden Age and extended right into his nineties. He was the second author, after Robert A. Heinlein, to be named a Grand Master of Science Fiction by SFWA, and by far the oldest recipient of the Hugo (2001, aged 93) and Nebula (2002, aged 94) awards. A significant voice in SF for over six decades, Jack Williamson is credited with inventing the terms 'terraforming' and 'genetic engineering'. He died in 2006.