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.