Actually there was an old Doctor Who story from 1978 about that. The story was called The Pirate Planet. This planet was run by Queen Xanxia. She was dying but created these things called "time dams" to suspend her in the last moments of her life. To power the time dams, she hollowed out her planet and jumped her planet across the universe in hyperspace to swallow smaller planets whole and devour them, population and all. Some of the power was used to create a holographic clone of herself which was slowly taking corporeal form. Her plan was to eventually stabilize her clone with the massive energy the planet was devouring and then let her original body die.
she ran into a problem in that as the populations of entire planets got devoured, their souls would haunt her world and unleash immense psychic power causing some of her own people to change into super psychic beings who wanted to stop her.