C. S. Lewis
After his conversion to theism in 1929, Lewis converted to Christianity in 1931, following a long discussion and late-night walk with his close friends Tolkien and Hugo Dyson. He records making a specific commitment to Christian belief while on his way to the zoo with his brother. He became a member of the Church of England – somewhat to the disappointment of Tolkien, who had hoped that he would join the Catholic Church.
Mount Doom
Reviewer Bart Higgins noted the similarity between Tolkien's Mount Doom and the volcanic caverns under Venus depicted in "Perelandra" by Tolkien's friend C.S. Lewis. "In both cases, the book reaches a cataclysmic scene of a struggle in an underground cavern, ending with an evil being falling into volcanic fire and being consumed. Since it is well known that Tolkien and Lewis frequently shared with each other their respective works in progress, it is reasonable to assume that the resemblance is no coincidence".