J.R.R. Tolkien’s close friend and fellow author was C.S. Lewis.
Tolkien and Lewis met at Oxford in 1926 and became members of a literary circle known as the Inklings. The group met chiefly at Oxford’s Eagle and Child pub and in Lewis’s rooms at Magdalen College, where members read and discussed works in progress. Tolkien’s The Lord of the Rings and Lewis’s space trilogy were among the works associated with this circle.
Lewis became an important early supporter of Tolkien’s fiction. Tolkien read sections of his developing mythology and The Lord of the Rings aloud to the group, receiving criticism and encouragement. Lewis’s enthusiasm helped sustain Tolkien during the long process of writing and revision.
Their friendship later became strained in some respects, including differences over religion and personal matters, but they remained significant figures in each other’s intellectual lives. Charles Williams and Owen Barfield were also Inklings, so they are plausible alternatives, but neither was Tolkien’s best-known fellow fantasy author.