The fictional planet ruled by the eldila in C.S. Lewis’s novel Perelandra is Perelandra.
Perelandra is the second novel in Lewis’s Space Trilogy, also known as the Ransom Trilogy. It was published in 1943 and follows philologist Elwin Ransom after he is transported to the planet Perelandra, which is identified with Venus.
The planet is portrayed as a world of floating islands and newly emerging life. Ransom encounters a Green Lady and faces a tempter who seeks to repeat the pattern of humanity’s fall in a new world.
The eldila are nonhuman spiritual beings connected with the planets. In the trilogy’s terminology, Perelandra is the name of both the novel and its setting, whereas Malacandra is the name used for Mars in Out of the Silent Planet. Thulcandra refers to Earth, making these names a frequent source of confusion.